Author name: doctorsrevision@gmail.com

Lesson focus: Bulk-forming laxatives are hydrophilic fibre agents that absorb water, form a soft bulky gel and stimulate physiological colonic propulsion. They are usually the safest drug class for suitable patients with chronic constipation—but only when obstruction has been excluded and sufficient fluid can be taken. Source coverage: The supplied laxatives lecture is used as the foundation: definition and causes of constipation; non-drug management; laxative classification; bulk agents, mechanism, examples, onset, adverse effects, fluid requirement, contraindication screening and counselling. Slides on emollient, osmotic, saline and stimulant laxatives are reserved for their own posts to avoid compressing or mixing topics. Learning objectives Define constipation; identify reversible causes and red flags; explain how bulk-forming laxatives work; compare psyllium/ispaghula, methylcellulose, wheat bran and polycarbophil; prescribe and counsel safely; recognise obstruction and dysphagia hazards; and distinguish when a different laxative class or urgent assessment is needed. 1. Constipation: symptom first, diagnosis second Constipation means infrequent, difficult or unsatisfactory evacuation. A patient may report fewer than three spontaneous bowel movements weekly, hard stools, straining, painful defecation, a sense of incomplete emptying or a need for manual manoeuvres. It is a symptom, not a disease. Common contributors Examples to ask about Diet/lifestyle Low fibre intake, reduced mobility, altered routine, reduced food intake Medicines Opioids, anticholinergics, iron, calcium, aluminium antacids, some antidepressants/antipsychotics, diuretics Medical causes Hypothyroidism, diabetes/autonomic dysfunction, hypercalcaemia, neurological disease, depression Structural/urgent causes Colorectal cancer, stricture, faecal impaction, volvulus or bowel obstruction 2. Assessment before a laxative Do not give bulk fibre blindly. Nausea/vomiting, significant abdominal pain/distension, inability to pass flatus, rectal bleeding, fever, acute change in bowel habit, weight loss, iron-deficiency anaemia or suspected obstruction requires clinical assessment—not self-treatment with a laxative. Take a bowel history: usual frequency and stool form, duration, hydration, diet, activity, pregnancy, co-medicines, previous surgery, neurological disease, swallowing difficulty and alarm features. Examine when indicated; assess dehydration, abdomen and rectum/impaction according to clinical setting. The Bristol Stool Form Scale can help define the problem and response to treatment. 3. Non-drug management: use evidence sensibly Increase dietary fibre gradually toward an appropriate intake through whole grains, legumes, vegetables, fruit and other locally available foods, unless a low-fibre diet is medically required. Regular meals, privacy/time for toileting and responding to the urge to defecate help establish a bowel routine. Physical activity has broad health benefit, but do not promise that exercise alone will cure severe constipation. Fluid should match the patient’s clinical needs. The supplied lecture correctly warns that telling every patient to drink excessive fluid is unsafe in heart failure or renal failure; bulk agents specifically still require adequate fluid with each dose. Review/remove a constipating medicine when clinically possible. 4. What are bulk-forming laxatives? Bulk-forming agents are indigestible or poorly digested hydrophilic colloids/fibres. They retain water in the intestinal lumen, creating a soft, larger stool mass. Distension activates stretch receptors and promotes normal peristaltic reflexes. They do not directly stimulate colonic nerves and do not rapidly purge the bowel. Psyllium / ispaghula Soluble fibre from Plantago husk. Forms a viscous gel; may also be used as dietary soluble fibre. Methylcellulose Semi-synthetic cellulose fibre; absorbs water and increases stool bulk. Calcium polycarbophil Synthetic hydrophilic polymer; swells by binding water. Wheat bran/dietary fibre Food-based fibre approach; increase gradually to limit gas and bloating. Expected onset and treatment goal Bulk agents work slowly—typically 12–72 hours, often 2–3 days with regular use. The goal is a soft, formed stool passed without excessive straining, not watery diarrhoea. They are unsuitable when rapid bowel evacuation is needed. 5. Indications and appropriate use Chronic functional constipation when obstruction and alarming causes are not suspected. Constipation associated with inadequate fibre intake or reduced stool bulk. Selected patients with irritable bowel syndrome with constipation, using dose adjustment according to symptoms; bloating may limit use. Patients who should avoid straining, after clinical assessment—for example painful anorectal conditions—when fibre is appropriate. Selected mild constipation in pregnancy, after checking diagnosis and obstetric guidance. Not a default answer: bulk fibre is often a sensible first option for chronic constipation, but it can worsen pain, impaction or obstruction when used in the wrong patient. Opioid-induced constipation, severe slow-transit constipation, faecal impaction and neurogenic bowel commonly need a different, individualised plan. 6. Administration: the fluid rule is a safety rule Read the exact product directions because sachets, powders, granules and capsules differ. Mix powder/granules with the recommended amount of water or other permitted liquid; stir and drink promptly before it thickens. Take each dose with at least 240 mL (8 ounces) of fluid unless a clinician has specified otherwise. Do not swallow bulk powder dry and do not give to someone unable to swallow safely. Start low and increase gradually to reduce bloating and flatulence. Separate oral prescription medicines by at least 2 hours before or after psyllium unless product information/advice says otherwise; fibre can affect absorption. Choking/oesophageal obstruction: psyllium and other swelling agents can obstruct the throat or oesophagus when taken with too little fluid or by a patient with dysphagia. Chest pain, vomiting, trouble swallowing or breathing after a dose is an emergency. 7. Adverse effects, contraindications and precautions Issue Why it happens Response Bloating, flatulence, abdominal distension Fibre fermentation and increased stool bulk Start low, increase gradually; reassess if severe or persistent Faecal impaction/obstruction Insufficient fluid, severe constipation, narrowed bowel or impaired motility Stop and assess urgently if pain, vomiting, distension or no flatus Choking/oesophageal obstruction Dry administration or dysphagia Never swallow dry; avoid in dysphagia; emergency assessment for symptoms Reduced medicine absorption Binding/delayed GI absorption Separate doses and check medicines individually Allergy Psyllium exposure can sensitise some people Stop and treat/refer for rash, wheeze, swelling or anaphylaxis symptoms Avoid or seek specialist advice in suspected bowel obstruction, faecal impaction needing disimpaction, acute surgical abdomen, dysphagia/oesophageal narrowing, severe colonic stricture, marked abdominal pain/nausea/vomiting, and where fluid intake is restricted or cannot be safely maintained. 8. Interactions and monitoring Bulk agents may delay or reduce absorption of oral medicines. The practical default is separation by at least 2 hours, then check high-risk medicines

Lesson focus: Proton-pump inhibitors (PPIs) are the most potent commonly used gastric acid suppressants. They are invaluable when the indication is correct, but a PPI is not a harmless “stomach tablet,” does not treat every abdominal complaint, and must not delay urgent investigation of bleeding, dysphagia, weight loss or persistent vomiting. Source coverage: This lesson covers every clinical teaching point in the supplied 21-slide PPI lecture—proton pump physiology, prodrug activation, all listed PPIs, irreversible mechanism, food timing, pharmacokinetics, short- and long-term adverse effects, medical/therapeutic uses and comparison—then extends it with current safety, interaction, monitoring and deprescribing practice. Learning objectives Explain the parietal-cell proton pump; describe how PPIs are activated and why they are taken before food; compare omeprazole, esomeprazole, lansoprazole, pantoprazole and rabeprazole; select appropriate indications; identify important interactions and adverse effects; manage long-term use safely; and distinguish acid suppression from definitive management of H. pylori, NSAID injury and GI bleeding. 1. The gastric proton pump: the final common pathway The H⁺/K⁺-ATPase is an integral membrane protein on the secretory canaliculus of the gastric parietal cell. Using ATP, it exchanges intracellular H⁺ for luminal K⁺ and is the final step in hydrochloric-acid secretion. Histamine (H₂), gastrin (CCK-B) and acetylcholine (M₃) stimulate the parietal cell through different upstream signals, but all converge on activation and insertion of this proton pump. Key consequence: an H₂ blocker reduces one upstream stimulant. A PPI inhibits the final common pump itself, so it produces deeper and more sustained acid suppression. 2. What are PPIs? PPIs are substituted benzimidazole prodrugs. They are acid-labile, so oral formulations are usually gastro-resistant/delayed-release. After absorption in the small intestine, the drug reaches parietal cells via the bloodstream and concentrates in their intensely acidic secretory canaliculi. There it is protonated and converted to an active sulfenamide. The active sulfenamide forms covalent disulfide bonds with sulfhydryl groups on H⁺/K⁺-ATPase. The pump is therefore irreversibly inhibited; recovery needs synthesis/insertion of new pumps. This explains why the plasma half-life is short but acid suppression lasts much longer. Mechanism in steps Enteric-coated PPI passes through the acidic stomach. It is absorbed in the small intestine and reaches parietal cells through the circulation. Active acid secretion creates acidic canaliculi. The prodrug becomes a reactive sulfenamide in that acidic compartment. The sulfenamide covalently binds H⁺/K⁺-ATPase. Acid secretion remains suppressed until new pumps are made. Do not confuse “irreversible pump binding” with permanent cure. The body replaces pumps; symptoms and acid secretion return after treatment is stopped. Long-term treatment requires an ongoing indication and review. 3. Why timing matters PPIs work best when pumps are being activated by a meal. For most standard once-daily regimens, take the dose about 30–60 minutes before breakfast. If a specialist-directed twice-daily regimen is used, take doses before breakfast and before the evening meal. Swallow delayed-release formulations whole unless the specific product instructions say otherwise. Wrong assumption Why it fails Safe teaching “It works immediately like an antacid.” Only actively secreting pumps are inhibited; maximal effect develops over several doses. Explain that response may build over days; use the prescribed schedule. “Take it after any meal.” Activation/timing is less reliable. Take before the meal, not as an after-meal rescue tablet. “A short half-life means a short effect.” Covalent pump inhibition persists after plasma drug is cleared. Short plasma half-life, longer acid-suppressive action. 4. Clinically used PPIs Omeprazole Widely available prototype. CYP2C19 inhibition makes clopidogrel interaction clinically important. Esomeprazole S-enantiomer of omeprazole. Also avoid with clopidogrel unless a specialist directs otherwise. Lansoprazole Common option; use product-specific instructions and interaction review. Pantoprazole Often selected when a lower CYP2C19-interaction burden is desired; still check all interactions. Rabeprazole Alternative PPI; availability varies by formulary. How to compare PPIs correctly Older tables sometimes list exact bioavailability, Cmax, protein binding and “no interactions” for a drug. Do not use such a table as a prescribing guarantee. Formulation, dose, CYP2C19 phenotype, hepatic function, indication and co-medicines matter. For everyday practice, the most useful comparison is indication, access/cost, timing/adherence, hepatic impairment and interaction risk—especially clopidogrel with omeprazole/esomeprazole. 5. Pharmacokinetics and special pharmacology Most PPIs have a plasma half-life of roughly 0.5–2 hours, but pump inhibition causes a much longer pharmacodynamic effect. Food can delay or reduce absorption of several formulations; the pre-meal instruction is clinically important. Once-daily dosing usually does not cause major accumulation in chronic renal failure, but the patient’s diagnosis, safety risks and other medicines still require review. Hepatic impairment can reduce clearance, particularly for esomeprazole and lansoprazole; consult current product information and use lower/limited doses where recommended. All PPIs reduce gastric acidity and can change absorption of pH-dependent medicines. 6. Indications: choose the diagnosis, not the habit 6.1 Gastro-oesophageal reflux disease (GORD/GERD) For classic heartburn and regurgitation without alarm symptoms, an appropriate time-limited PPI trial is common. PPIs are more effective than H₂ blockers for healing erosive oesophagitis. If symptoms resolve, review whether the patient can step down, stop or use the lowest effective regimen unless there is a durable indication such as severe erosive disease, Barrett’s oesophagus in selected patients or specialist-directed therapy. 6.2 Peptic ulcer disease PPIs promote healing of gastric and duodenal ulcers. However, ulcer therapy must identify the cause: H. pylori: test and give a current, locally appropriate eradication regimen. A PPI is an acid-suppression component; it is not eradication treatment alone. NSAID ulcer: stop/reduce NSAID exposure where possible, assess aspirin indication, test/treat H. pylori when appropriate, and provide evidence-based gastroprotection when ongoing risk remains. Bleeding ulcer: resuscitation, referral/endoscopy and protocol-based management are required. A community prescription alone is not definitive treatment. 6.3 Dyspepsia Dyspepsia is a symptom complex, not a diagnosis. Use short empirical PPI treatment only after assessing alarm features and likely causes. In suitable adults, a validated H. pylori test-and-treat strategy may be preferred. PPIs can cause false-negative urea-breath and stool-antigen tests; follow the local protocol for stopping PPIs before testing. 6.4 NSAID-related ulcer prevention Patients at increased GI-bleeding risk who must continue an NSAID or antiplatelet regimen may require PPI gastroprotection. Risk increases with previous ulcer/bleed, older age, high-dose

Lesson focus: Histamine H₂-receptor antagonists (H₂ blockers/H₂RAs) reduce gastric acid secretion. They remain useful for selected dyspepsia, reflux and ulcer-related situations, but they are not interchangeable with proton-pump inhibitors (PPIs), do not eradicate Helicobacter pylori, and must not delay assessment of gastrointestinal bleeding or cancer warning signs. Source coverage: This lesson incorporates the supplied H1 & H2 receptor antagonist lecture’s histamine foundations, receptor distribution, H₂-blocker definition, named medicines, mechanism, adverse effects, medicinal-chemistry/SAR points and clinical uses. The lecture’s detailed H₁-blocker slides are dealt with in the separate antihistaminics lesson so that this GI lesson remains clinically coherent. Learning objectives By the end of this lesson, the learner should be able to explain histamine’s role in acid secretion; distinguish H₁, H₂, H₃ and H₄ receptors; classify H₂ blockers; compare cimetidine, famotidine, nizatidine and ranitidine; select appropriate clinical uses; recognise when an H₂ blocker is insufficient; prevent important interactions and adverse effects; and counsel a patient safely. 1. Core foundation: histamine and the gastric parietal cell Histamine is an endogenous autacoid and neurotransmitter formed by decarboxylation of the amino acid histidine. It is stored especially in mast cells and basophils, and is present in the skin, respiratory and gastrointestinal mucosa, brain and other tissues. Its actions depend on receptor subtype; therefore an “antihistamine” is not one single clinical group. Receptor Main sites Key effects Clinical link H₁ Endothelium, smooth muscle, sensory nerves, CNS Itching, increased vascular permeability, bronchoconstriction, allergic symptoms Blocked by H₁ antihistamines for allergy/urticaria H₂ Gastric parietal cells; also heart, vascular and immune cells Stimulates gastric acid secretion Blocked by H₂ blockers for acid reduction H₃ Presynaptic CNS and peripheral nerves Modulates histamine and other neurotransmitter release Not a peptic-ulcer drug target H₄ Bone marrow and immune cells Immune-cell chemotaxis and inflammation Not a routine GI-drug target How acid is produced Three principal stimulants act synergistically on the gastric parietal cell: acetylcholine from vagal nerves at M₃ receptors, gastrin at CCK-B receptors, and histamine released by enterochromaffin-like (ECL) cells at H₂ receptors. H₂ activation couples through Gs to adenylate cyclase, raises intracellular cAMP and activates protein kinase A. This increases activity of the final common pathway, the apical H⁺/K⁺-ATPase (proton pump), which secretes H⁺ into the stomach lumen. Why H₂ blockade works: blocking histamine at the parietal-cell H₂ receptor reduces cAMP-mediated acid secretion and also weakens the potentiating effect that histamine normally has on acetylcholine and gastrin. It is therefore an indirect reduction of proton-pump output. PPIs inhibit the pump itself and usually suppress acid more profoundly. 2. What are H₂-receptor antagonists? H₂ blockers are reversible, competitive antagonists at parietal-cell H₂ receptors. They reduce basal and stimulated gastric acid secretion, particularly basal and nocturnal acid output. They also reduce pepsin secretion secondarily because pepsin activity depends on an acidic environment. Cimetidine Prototype H₂ blocker. Most interaction-prone and most endocrine adverse effects. Famotidine Common modern choice where available; little CYP inhibition but adjust in renal impairment. Nizatidine H₂ blocker with few CYP interactions; availability varies. Ranitidine Historical drug. Do not assume it is available or appropriate: many markets withdrew products because of NDMA impurity concerns. Important correction to a common phrase H₂ blockers are sometimes loosely called “antihistamines,” but in peptic-ulcer practice they are acid-suppressing H₂ antagonists, not H₁ allergy medicines. An H₁ blocker such as chlorpheniramine does not treat a peptic ulcer by blocking parietal-cell H₂ receptors. 3. Pharmacodynamics: what H₂ blockers can and cannot do They lower gastric volume and hydrogen-ion concentration, raise intragastric pH and promote healing of many uncomplicated acid-related ulcers. They are especially useful when symptoms are nocturnal or intermittent because histamine has a prominent role in nocturnal acid secretion. They are less potent than PPIs for severe erosive oesophagitis, high-risk upper-GI bleeding and strong continuous acid suppression. Tolerance (tachyphylaxis) may develop with regular continuous use, often after days to weeks. This makes persistent daily symptoms a reason to reassess the diagnosis and treatment plan rather than simply escalating indefinitely. They give symptomatic acid relief; they do not eradicate H. pylori, replace endoscopic haemostasis in bleeding ulcer, or remove the ulcerogenic effect of ongoing NSAID exposure. 4. Medicinal-chemistry/SAR principles from the supplied lecture The H₂ antagonists were developed by modifying histamine to preserve receptor recognition while converting agonist activity into competitive antagonism. The imidazole ring is not mandatory: heterocyclic rings such as furan, thiophene and thiazole can support H₂-receptor selectivity and potency. A flexible side chain separates the heterocyclic ring from a polar, relatively non-basic terminal group. The lecture emphasises an approximately four-atom separation between ring and terminal nitrogen and notes thioether/isosteric linkages in several molecules. Clinical translation: medicinal chemistry explains why these drugs bind H₂ receptors, but prescribing decisions depend on potency, renal function, CYP interaction burden, availability, indication and patient risk—not on structure alone. 5. Individual drugs: compare before you prescribe Drug Key characteristics Major cautions Practical place Cimetidine Oldest prototype; inhibits several CYP enzymes and can increase concentrations of interacting medicines Gynecomastia, sexual dysfunction, galactorrhoea, confusion in older/renal-impaired patients, many interactions Usually avoided when a lower-interaction H₂ blocker is available Famotidine Potent; minimal CYP inhibition Reduce dose/extend interval in renal impairment; CNS effects and QT-risk concern are greater when drug accumulates Often preferred H₂ blocker for intermittent/nocturnal symptoms Nizatidine Few CYP interactions; availability varies Renal elimination: dose-adjust in renal impairment; check local formulary Alternative where stocked Ranitidine Previously widely used, fewer interactions than cimetidine NDMA-related market withdrawal/restrictions in many jurisdictions; never prescribe from outdated notes without checking national regulatory status Historical/exam knowledge only unless confirmed locally authorised 5.1 Cimetidine: the interaction and endocrine drug Cimetidine competitively blocks H₂ receptors but also inhibits hepatic microsomal drug metabolism, notably CYP-mediated pathways. It can raise levels of medicines with narrow therapeutic windows or dose-related toxicity. Always obtain a complete medication history, including warfarin, phenytoin, theophylline, some antiarrhythmics and other locally used medicines. The exact interaction depends on the co-medicine; check an interaction reference rather than memorising an incomplete list. Endocrine/antiandrogenic effects: gynecomastia, reduced libido, erectile dysfunction and occasionally galactorrhoea, particularly with high dose or prolonged

Lesson focus: Immunosuppressants deliberately reduce harmful cellular, humoral or both immune responses. Their life-saving roles include prevention and treatment of transplant rejection and control of severe autoimmune/inflammatory disease. Their predictable cost is infection, malignancy, organ toxicity, cytopenia, reproductive risk and drug-interaction burden. Clinical rule: Never prescribe an immunosuppressant as an isolated drug name. State the indication, target immune pathway, baseline infection screen, monitoring plan, interactions, pregnancy plan and red flags. Learning objectives Explain T-cell activation and the sites of action of immunosuppressants; classify individual drugs; compare calcineurin inhibitors, mTOR inhibitors, antiproliferatives, glucocorticoids and biologics; outline transplant induction, maintenance and rejection treatment; and recognise major adverse effects, interactions and monitoring needs. 1. Definition and major uses Immunosuppressants inhibit cellular immunity, humoral immunity or both. They are used to prevent allograft rejection after kidney, liver, heart and other transplants; to treat acute rejection; and to control autoimmune or inflammatory disorders such as rheumatoid arthritis, systemic lupus erythematosus, inflammatory bowel disease, psoriasis, uveitis, myasthenia gravis and some vasculitides. The precise drug choice varies by disease, severity, organ function, pregnancy potential, infections, local availability and specialist guideline. Balance, not elimination: inadequate suppression risks graft rejection or uncontrolled immune disease; excessive suppression risks opportunistic infection, sepsis, cancer and toxicity. Combination treatment uses different pathways so that each component can often be given at a lower dose. 2. T-cell activation: the mechanism map The supplied lecture correctly centres on helper-T-cell activation. An antigen-presenting cell (APC) displays peptide on MHC class II to the T-cell receptor/CD4 complex. Co-stimulatory signals are also required. T-cell receptor signalling activates phospholipase C, generating DAG and IP3. IP3 raises intracellular calcium; calcium-calmodulin activates calcineurin. Calcineurin dephosphorylates NFAT, allowing NFAT to enter the nucleus and promote IL-2 and other cytokine-gene transcription. IL-2 then drives T-cell proliferation. Site in immune response Drug approach Examples Antigen presentation/cytokine production Broad anti-inflammatory suppression Glucocorticoids Calcineurin → NFAT → IL-2 transcription Calcineurin inhibition Cyclosporine, tacrolimus IL-2 receptor growth signalling mTOR inhibition or IL-2R blockade Sirolimus/everolimus; basiliximab Purine/pyrimidine synthesis and DNA replication Antiproliferative therapy Azathioprine, mycophenolate, methotrexate TNF, IL-1, lymphocyte surface targets Biological targeted suppression/depletion Anti-TNF agents, anakinra, ATG, anti-CD antibodies 3. Classification Calcineurin inhibitors Cyclosporine; tacrolimus. mTOR inhibitors Sirolimus; everolimus. Antiproliferatives Azathioprine; mycophenolate; methotrexate. Glucocorticoids Prednisolone; methylprednisolone and others. Biological agents Anti-TNF, IL-1 blockade, IL-2R antibodies, T-cell-depleting globulins and other monoclonal antibodies. 13. Practical monitoring by drug class Class Before starting During treatment Do not miss Calcineurin inhibitor Renal function, BP, electrolytes, glucose, interaction review Trough level, creatinine/eGFR, K+, Mg2+, BP, glucose Nephrotoxicity, neurotoxicity, hyperkalaemia, interacting antimicrobials mTOR inhibitor CBC, lipids, wound status, renal/liver assessment Drug level, CBC, lipids, urine protein, lung symptoms Cytopenia, dyslipidaemia, poor wound healing, pneumonitis Azathioprine CBC, liver tests, TPMT/NUDT15 where available, allopurinol/febuxostat review CBC and liver tests regularly Marrow suppression, pancreatitis, infection Mycophenolate CBC, renal/liver tests, pregnancy plan CBC, diarrhoea, infection, pregnancy prevention Severe infection, leucopenia, embryo-fetal toxicity Methotrexate CBC, renal/liver tests, pregnancy assessment, alcohol/lung history CBC, LFTs, creatinine, mouth/lung symptoms Weekly dosing, pneumonitis, marrow/liver toxicity Biologic TB/hepatitis screen, CBC/LFTs, vaccination review Infection surveillance and disease-specific tests Reactivation of latent infection; avoid live vaccine where contraindicated 14. Special situations Pregnancy and conception Every immunosuppressant requires a deliberate pregnancy discussion. Mycophenolate and methotrexate have substantial embryo-fetal risk and demand specialist-directed contraception and pre-conception switching. Azathioprine, tacrolimus and corticosteroids may sometimes be used in pregnancy for a compelling indication, but that is a specialist risk-benefit decision—not an invitation to self-continue or self-stop. Uncontrolled transplant rejection or autoimmune disease can itself endanger parent and fetus. Infection and vaccination Do not wait for a patient to become septic before considering infection prevention. Check vaccine history before planned long-term suppression, use inactivated vaccines appropriately, and avoid live vaccines during major immunosuppression unless specialist advice says otherwise. Fever, weight loss, persistent cough, dysuria, diarrhoea, shingles-like rash, oral ulcers or unexplained bruising require prompt review. In Uganda and other high-TB-burden settings, TB evaluation before anti-TNF therapy is a practical safety requirement. Adherence and access For transplant recipients, missed doses can cause graft rejection; doubled doses can cause toxicity. Patients should keep an updated medicine list, use one pharmacy where possible, report stock interruptions early and contact the transplant/medical team before taking herbal remedies, antibiotics, antifungals, anticonvulsants or NSAIDs. A “normal” single lab result does not exclude rejection or infection—interpret symptoms, levels, trends and graft-specific findings together. 15. Final summary Immunosuppressants work at defined stages of immune activation: calcineurin inhibitors prevent IL-2 transcription; mTOR inhibitors block IL-2-driven proliferation; antiproliferatives limit lymphocyte expansion; corticosteroids broadly suppress inflammatory transcription; and biological agents block cytokines or deplete/disable lymphocytes. The same mechanisms that protect a graft or control autoimmunity create predictable risks. Safe practice combines the right regimen, screening, therapeutic monitoring, interaction control, reproductive planning and rapid response to infection or toxicity. 4. Calcineurin inhibitors 4.1 Cyclosporine Cyclosporine is a cyclic polypeptide that enters T cells and binds the immunophilin cyclophilin. The cyclosporine-cyclophilin complex inhibits calcineurin, preventing NFAT activation, reducing IL-2 transcription and suppressing T-cell proliferation. The lecture’s G0/G1 arrest teaching point is useful: calcineurin inhibitors predominantly block early T-cell activation rather than directly destroying lymphocytes. Uses: transplant prophylaxis and selected autoimmune disease. Modern disease-specific indications differ; do not use an old list alone. Adverse effects: nephrotoxicity, hypertension, hyperkalaemia, neurotoxicity/tremor, hyperuricaemia, dyslipidaemia, gingival hyperplasia, hirsutism, diabetes risk, infection and malignancy. Monitor blood pressure, renal function, electrolytes, glucose/lipids and trough drug levels where required. 4.2 Tacrolimus Tacrolimus is chemically distinct but has the same final calcineurin target. It binds FKBP rather than cyclophilin; the tacrolimus-FKBP complex inhibits calcineurin. It is more potent by weight than cyclosporine, but that does not make it automatically “better”—drug selection and target trough range are transplant-program decisions. Compare with cyclosporine: both cause nephrotoxicity, hypertension, neurotoxicity, hyperkalaemia, infection and malignancy. Tacrolimus commonly causes tremor and diabetes; cyclosporine more characteristically causes hirsutism and gingival hyperplasia. Both have highly important CYP3A/P-glycoprotein interactions and need therapeutic drug monitoring. Interaction trap: macrolides such as erythromycin/clarithromycin, azole antifungals, grapefruit products and other CYP3A inhibitors can raise calcineurin-inhibitor levels and toxicity. Rifampicin, certain anticonvulsants and other enzyme

Scope of this lesson: Immunostimulants are medicines, biological products or cell-based treatments that deliberately increase, direct or restore a useful immune response. They are used very differently in vaccination, selected immunodeficiency states, prevention of chemotherapy-related neutropenia, chronic granulomatous disease, bladder cancer, multiple myeloma and specialised cancer immunotherapy. They are not general “immune boosters” for self-medication. Safety principle: A stronger immune response can help control infection or cancer, but it can also cause fever, inflammation, autoimmunity, capillary leak, thrombosis, infusion reactions or life-threatening cytokine toxicity. The indication, product, route and monitoring plan matter. Learning objectives After this lesson, the student should be able to describe innate and adaptive immune responses; classify immunostimulant approaches; explain active and passive immunisation; discuss microbial products, BCG, cytokines, colony-stimulating factors, immunoglobulins, historical small-molecule agents and modern cellular therapy; and prescribe or counsel safely within the limits of local guidelines and specialist care. 1. What are immunomodulators and immunostimulants? Immunomodulators alter immune activity. They include drugs that suppress an excessive response (for example after transplantation or in autoimmune disease) and drugs that enhance, redirect or replace a protective response. Immunostimulants are the latter group: they increase one or more arms of immune defence, haematopoiesis or tumour-directed immunity. That definition must be applied precisely. A vaccine stimulates antigen-specific immune memory; intravenous immunoglobulin supplies ready-made antibodies and is therefore a form of passive immunisation rather than a direct stimulant of the patient’s own lymphocytes; filgrastim stimulates neutrophil production; intravesical BCG creates a local anti-tumour immune reaction in the bladder; and CAR-T therapy gives a patient modified cells able to recognise cancer. These are not interchangeable therapies. Approach What is enhanced or provided? Typical example Immediate effect? Active antigen-specific immunisation The patient’s own adaptive memory Vaccines No; protection develops over time Passive immunisation Preformed antibodies Rabies immunoglobulin, hepatitis B immunoglobulin, IVIG Yes, but temporary Innate/local immune stimulation Inflammatory and antigen-presenting activity Intravesical BCG Depends on clinical setting Cytokine/growth-factor therapy Specific immune-cell activation or blood-cell production Interferon-gamma, aldesleukin, filgrastim Variable; requires monitoring Cellular immunotherapy Expanded or engineered anti-tumour immune cells TIL therapy, CAR-T therapy Specialist therapy with major toxicities 2. Immune-response foundations: why immunostimulants work 2.1 Innate immunity The supplied lecture begins correctly with the innate response: it is the rapid first line of defence against an antigenic insult. It includes physical barriers such as skin and mucosal epithelium; biochemical defences including complement, lysozyme and interferons; and cellular defences including neutrophils, monocytes, macrophages, natural killer (NK) cells, mast cells and basophils. Innate cells recognise conserved microbial patterns called pathogen-associated molecular patterns (PAMPs) through pattern-recognition receptors such as Toll-like receptors. This triggers cytokine production, phagocytosis, killing of microbes and activation of antigen-presenting cells. It is useful in early infection, but uncontrolled innate activation can produce sepsis-like inflammation, hypotension, organ injury and shock. 2.2 Adaptive immunity Adaptive immunity is antigen-specific and generates memory. Humoral immunity is mediated by B lymphocytes and antibodies; it is especially important against extracellular microbes and toxins. Cell-mediated immunity is mediated mainly by T lymphocytes: CD4+ helper cells coordinate other immune cells, while CD8+ cytotoxic T cells kill infected or malignant cells. Regulatory T cells limit excessive responses. NK cells are innate lymphocytes but also contribute strongly to anti-viral and anti-tumour killing. Vaccines aim to create long-lived B-cell, T-cell and antibody memory. Cytokines may increase the number or activity of selected immune cells. BCG and adjuvants activate innate pathways and antigen presentation. Adoptive cell transfer bypasses some natural limitations by supplying a large number of tumour-reactive lymphocytes. 3. Classification of immunostimulant strategies Antigen-based approaches Vaccines and adjuvants produce active, specific immunisation and immune memory. Passive antibody approaches Normal human immunoglobulin and specific hyperimmune globulins provide immediate antibody protection or replacement. Microbial or microbial-derived products BCG and selected microbial products activate innate and adaptive anti-tumour or anti-infective responses. Cytokines and haematopoietic growth factors Interferons, interleukins and colony-stimulating factors alter immune signalling or blood-cell production. Small-molecule or peptide immunomodulators Thalidomide/related IMiDs, levamisole, inosine pranobex and thymic peptides have very different evidence, safety and availability. Cell-based immunotherapy TIL therapy, CAR-T cells, NK-cell approaches and dendritic-cell vaccines are specialist cancer treatments. 4. Microbial products and BCG 4.1 Why microbial products stimulate immunity Many bacterial products contain PAMPs. When recognised by antigen-presenting cells (APCs), they induce cytokines and co-stimulatory signals that strengthen T-cell and B-cell responses. This is the biological basis for using microbial components in vaccines and for using BCG as local cancer immunotherapy. It is also the reason these products can cause fever, inflammatory reactions and, rarely, severe systemic toxicity. 4.2 BCG: two completely different clinical uses BCG is a live attenuated strain derived from Mycobacterium bovis. Students must separate its vaccine role from its intravesical bladder-cancer role. BCG use Route/setting Purpose Core mechanism BCG vaccination Intradermal immunisation programme Protection against severe forms of tuberculosis, especially in children, according to national policy Active immune priming and cellular immune memory against mycobacterial antigens Intravesical BCG Instilled directly into bladder by trained urology team Treatment/prophylaxis of selected non-muscle-invasive bladder cancers after transurethral resection Local innate and T-cell-mediated anti-tumour inflammation The lecture states that BCG produces a granulomatous reaction and activates macrophages; this remains a useful teaching anchor. However, avoid the oversimplification that BCG only stimulates immunoglobulin production. Protection against tuberculosis and the anti-tumour effect both depend substantially on cell-mediated immune pathways. BCG vaccination is not a treatment for active tuberculosis and it is not automatically safe for every immunocompromised person. 4.3 Intravesical BCG: practical principles Intravesical BCG is a proven immune-system modulator for selected intermediate- and high-risk non-muscle-invasive bladder cancer. It is administered into the bladder, not injected intravenously. It is commonly used after transurethral resection of a bladder tumour to lower recurrence and progression risk in appropriately selected patients. Treatment must be guided by urology/oncology protocols. Expected local/systemic effects: dysuria, frequency, urgency, haematuria, malaise, low-grade fever and flu-like symptoms. Important complications: severe cystitis, granulomatous inflammation, hypersensitivity reaction and rare disseminated BCG infection/sepsis. Red flags after treatment: persistent high fever, rigors, hypotension, respiratory symptoms, jaundice or severe systemic illness require urgent assessment. Do

Lesson focus: Mast-cell stabilisers are preventive anti-allergic medicines. They reduce the release of chemical mediators from sensitised mast cells, helping to prevent symptoms before they start. They are not bronchodilators, do not reverse an established acute asthma attack, and must never replace emergency treatment for anaphylaxis. Core idea: Use these medicines regularly or before a predictable trigger. They work best as prevention, not rescue. Learning objectives By the end of this lesson, the student should be able to explain mast-cell activation in allergy; classify the mast-cell stabilisers; describe the mechanisms, routes, uses, adverse effects and limitations of individual agents; distinguish prophylaxis from reliever treatment; and counsel a patient safely on inhaled, nasal and ophthalmic preparations. 1. Where mast-cell stabilisers fit in allergic disease Allergic disease begins when a sensitised person encounters an allergen again. Examples include house-dust mite, pollen, animal dander, mould, occupational sensitizers, exercise in a susceptible patient, cold air, smoke and other airway irritants. In asthma, the consequences include bronchial smooth-muscle contraction, mucosal oedema and increased mucus secretion. Together, these narrow the airways and cause wheeze, breathlessness, cough and chest tightness. Mast-cell stabilisers are traditionally grouped among the preventive anti-asthmatic drugs. The supplied anti-asthmatic-drugs lecture correctly places them beside bronchodilators, leukotriene antagonists, glucocorticoids and anti-IgE therapy, but their action is distinct: Drug group Main action Role in an acute attack Short-acting beta2-agonist (for example salbutamol) Rapid bronchodilation Reliever treatment; use according to the acute-asthma plan Inhaled corticosteroid Broad anti-inflammatory controller effect Not an immediate bronchodilator; key long-term controller therapy Leukotriene receptor antagonist Blocks cysteinyl-leukotriene effects Preventive add-on in selected patients Mast-cell stabiliser Reduces mediator release from mast cells No: not a rescue bronchodilator Adrenaline Alpha- and beta-adrenergic effects Essential first-line treatment for anaphylaxis; not routine chronic-asthma controller therapy Do not confuse prevention with treatment of deterioration. A patient with severe breathlessness, inability to speak full sentences, cyanosis, exhaustion, altered consciousness, silent chest or poor response to a reliever needs urgent assessment and acute-asthma treatment. Do not delay this while giving cromoglicate or another mast-cell stabiliser. 2. Mast cells and the allergic response Mast cells are immune cells found in tissues that interface with the environment, including the skin, nasal mucosa, conjunctiva, gastrointestinal tract and respiratory mucosa. Their granules contain preformed mediators, especially histamine. They also generate newly synthesised mediators after activation. Sensitisation and re-exposure: the examination sequence First exposure: an allergen stimulates a type-2 immune response and production of allergen-specific IgE. Sensitisation: IgE binds high-affinity Fc epsilon RI receptors on mast cells and basophils. Re-exposure: the allergen cross-links adjacent IgE molecules on the mast-cell surface. Activation: intracellular signalling and calcium-dependent processes lead to degranulation and mediator synthesis. Clinical effects: airway smooth-muscle contraction, increased vascular permeability and oedema, mucus secretion, itching, redness and recruitment of other inflammatory cells. Important mediators include histamine, cysteinyl leukotrienes (LTC4, LTD4 and LTE4), prostaglandins, platelet-activating factor, proteases and cytokines. Histamine contributes to itching, vasodilatation and increased vascular permeability. Leukotrienes are potent, sustained bronchoconstrictors and increase mucus production and mucosal oedema. This explains why an allergic symptom can be more than “histamine alone”. 3. Mechanism of mast-cell stabilisers Mast-cell stabilisers reduce the tendency of activated mast cells to release inflammatory mediators. Sodium cromoglicate (also called cromolyn sodium) is the prototype. Its full molecular mechanism is not represented by one simple receptor interaction, but clinically it is understood as reducing calcium-dependent mast-cell degranulation and mediator release. Effects on other inflammatory cells and airway sensory pathways may also contribute. The result is less release of histamine, leukotrienes, prostaglandins and other mediators after allergen or irritant exposure. Therefore these medicines can reduce bronchial hyper-responsiveness and prevent some symptoms induced by triggers. They do not directly relax contracted bronchial smooth muscle. Once major bronchospasm is established, their onset is too slow and their action is unsuitable for rescue. Memory line: Stabilise before the storm; do not expect it to open an already closed airway. 4. Drugs in this group Sodium cromoglicate / cromolyn sodium Prototype mast-cell stabiliser. Used locally by inhaled, nasal or ophthalmic routes; oral preparations may be used for selected gastrointestinal symptoms associated with mast-cell disease. Very little is absorbed systemically from most local preparations. Nedocromil sodium Pharmacologically similar preventive agent. It has had an inhaled role in asthma but availability varies greatly and it is now uncommon or discontinued in many settings. Ketotifen An orally active drug with both H1-antihistamine and mast-cell-stabilising properties. It is slow in onset and may cause sedation; do not describe it as an acute reliever. Ophthalmic mast-cell stabilisers Examples used in some settings include sodium cromoglicate, lodoxamide and pemirolast. Several modern eye preparations combine antihistamine activity with mast-cell stabilisation; local formulary availability differs. 5. Sodium cromoglicate in detail Pharmacokinetics and route Sodium cromoglicate is poorly absorbed from the gastrointestinal tract. This is why oral administration is not useful for ordinary asthma prevention, whereas inhaled delivery places the drug at the airway surface. Nasal sprays and eye drops deliver local treatment to the nose and conjunctiva. Low systemic absorption explains the generally favourable systemic safety profile, but it does not mean that the medicine is risk-free or that inhaler technique is unimportant. Asthma and trigger-induced bronchospasm In asthma, cromoglicate is a prophylactic medicine. It may be considered for prevention of symptoms in selected patients, including symptoms provoked predictably by allergens, exercise, cold air or inhaled irritants. It must be taken as prescribed and may be used before a known trigger when the product and clinical plan recommend this. It should not be used alone to manage an asthma exacerbation. Response is not immediate. Patients must be told that controller benefit may require regular use for days to weeks, and persistent symptoms require review of diagnosis, inhaler technique, exposure to triggers and the current anti-inflammatory regimen. In modern asthma care, inhaled corticosteroid-containing treatment is generally more effective for controlling airway inflammation, so cromoglicate has a limited, often historical role in many formularies. Allergic rhinitis Intranasal cromoglicate may reduce sneezing, rhinorrhoea and nasal itching when used regularly. It is a local preventive choice

Anti-allergic Agents Corticosteroids in allergy and airway disease: treat the inflammatory process, but always plan safety, route and stopping Corticosteroids are not simply “strong anti-allergy tablets.” They are adrenal hormones and synthetic analogues with major glucocorticoid and/or mineralocorticoid actions. In allergy, asthma, rhinitis, eczema and immune disease they suppress many inflammatory pathways more broadly than antihistamines. This can protect life and organs, but can also cause infection, diabetes, hypertension, osteoporosis, psychiatric disturbance, cataract/glaucoma and adrenal suppression. The safest treatment is the least systemic exposure that achieves the clinical objective: correct diagnosis, local route where possible, a defined duration, monitoring and an exit plan. Emergency allergy: steroid is an adjunct, not first-line lifesaving treatment In suspected anaphylaxis—airway compromise, breathing difficulty, shock or rapidly progressive multisystem reaction—give intramuscular adrenaline and emergency ABC management according to protocol. Corticosteroids have delayed genomic effects and must never delay adrenaline, oxygen, fluids, bronchodilator or urgent transfer. What this post adds to the SAIDs foundation The earlier SAIDs lesson explains general glucocorticoid pharmacology. This companion post exhausts the supplied 65-slide corticosteroid lecture through the clinical anti-allergic lens: adrenal physiology, potency/route selection, inhaled/nasal/topical/systemic use, asthma and allergic emergencies, infection precautions, steroid stewardship, tapering and patient counselling. It therefore supports students in choosing and monitoring treatment rather than memorising a long list of indications. 1. Adrenal cortex, biosynthesis and regulation The adrenal cortex forms steroid hormones from cholesterol. The zona glomerulosa produces mineralocorticoids (mainly aldosterone), the zona fasciculata produces glucocorticoids (mainly cortisol), and the zona reticularis produces adrenal androgens. ACTH is particularly important for cortisol synthesis; aldosterone is governed mainly by the renin–angiotensin–aldosterone system and plasma potassium. Axis or hormone Normal role Why it matters clinically CRH → ACTH → cortisol (HPA axis) Hypothalamic CRH stimulates pituitary ACTH; ACTH stimulates adrenal cortisol. Cortisol gives negative feedback. Exogenous systemic steroid suppresses CRH/ACTH. Abrupt cessation after significant exposure can leave inadequate endogenous cortisol. Circadian rhythm Cortisol is highest in early morning and lowest around midnight. When compatible with disease control, a single morning glucocorticoid dose better follows physiology and may reduce HPA suppression. Cortisol in stress Illness, trauma, surgery and severe inflammation require higher cortisol output. Patients dependent on replacement or at risk of adrenal suppression may need protocolled stress-dose cover; this is not optional “extra medicine.” Aldosterone Promotes distal sodium retention and potassium/hydrogen excretion. Mineralocorticoid activity explains oedema, hypertension, hypokalaemic alkalosis and heart-failure worsening with some steroids. 2. Physiological actions explain the adverse effects Glucocorticoid action Adaptive purpose Pharmacological excess Increased hepatic gluconeogenesis and reduced peripheral glucose utilisation Provides fuel during stress. Hyperglycaemia, insulin resistance and steroid-induced diabetes. Protein catabolism and amino-acid mobilisation Supplies substrate for hepatic synthesis. Proximal muscle weakness, wasting, thin skin, bruising, poor healing, negative nitrogen balance and bone loss. Fat mobilisation plus redistribution Energy availability. Truncal obesity, moon facies, dorsocervical fat pad and dyslipidaemia. Reduced gut calcium absorption/increased renal loss and reduced bone formation Not a desired treatment effect. Osteoporosis, fragility fractures, growth impairment and delayed repair. Maintains vascular response to catecholamines and GFR/water excretion Supports circulation during stress. Loss in adrenal insufficiency contributes to hypotension/collapse; excessive mineralocorticoid effect promotes fluid retention and BP rise. Suppresses immune-cell recruitment, cytokines and eicosanoids Limits excessive tissue injury. Infection susceptibility, muted inflammatory signs and reactivation of latent infection. 3. Anti-inflammatory and anti-allergic mechanism: why corticosteroids are broader than antihistamines Glucocorticoids enter cells and bind intracellular glucocorticoid receptors. The complex moves to the nucleus, changing gene expression. They increase anti-inflammatory proteins (including annexin A1/lipocortin) and repress NF-κB/AP-1-regulated inflammatory genes. This decreases phospholipase A2-driven arachidonic acid release, COX-2 expression, cytokines, adhesion molecules, chemotaxis, leucocyte migration, lysosomal enzymes, vascular permeability and mediator generation. Inflammatory target Corticosteroid effect Clinical outcome and limitation Eosinophils, T cells, macrophages and antigen presentation Reduced activation, survival, migration and cytokine production; lymphocyte redistribution/lympholysis. Controls allergic/autoimmune inflammation but impairs host defence. Prostaglandins, leukotrienes, PAF and cytokines Reduced production through upstream and transcriptional effects. More comprehensive anti-inflammatory effect than H1 antihistamine; delayed onset means it cannot substitute for adrenaline in anaphylaxis. Capillaries/lysosomes Reduced permeability/exudation and reduced lysosomal enzyme release. Less oedema and tissue damage; also delayed healing and masked infection. Fibroblasts/collagen repair Suppressed proliferation and repair. May reduce scarring in selected use, but causes thin skin/striae/poor wound healing and silent perforation risk in severe disease. 4. Individual corticosteroids: select by potency, duration and mineralocorticoid activity Drug Practical profile Typical roles from the supplied lecture Key caution Hydrocortisone Short acting; meaningful glucocorticoid and mineralocorticoid activity. Adrenal replacement/crisis protocols; selected acute severe inflammatory/allergic care, status asthmaticus pathways, topical or rectal formulations. Fluid/salt retention at pharmacological exposure; follow exact emergency/replacement protocol. Prednisone / prednisolone Intermediate acting, more glucocorticoid-selective than hydrocortisone; oral workhorse in many settings. Allergic and inflammatory conditions, autoimmune disease, malignancy and short oral courses for indicated asthma exacerbation. Prednisone requires hepatic activation; do not create repeated open-ended courses without review. Methylprednisolone Intermediate acting with low mineralocorticoid action; oral/IV preparations. Selected severe inflammatory disease, pulse regimens, transplant/renal/pemphigus and some IBD preparations. “Pulse” is a specialist/protocolled strategy, not simply a very high dose for ordinary symptoms. Triamcinolone Potent glucocorticoid used in topical, local and some intra-articular formulations. Selected inflammatory skin/joint applications. Exclude joint/skin infection; injection can still cause systemic glucose/HPA effects. Dexamethasone Potent, long acting and minimal mineralocorticoid action. Selected cerebral oedema, antiemetic, severe inflammatory/allergic and endocrine-test protocols. Long biological action means substantial HPA suppression risk; do not interchange casually with hydrocortisone. Betamethasone Potent long acting glucocorticoid. Specialist obstetric and inflammatory/dermatologic protocols. Route, timing and formulation matter; do not use as a generic “strong steroid.” Fludrocortisone Predominantly mineralocorticoid with some glucocorticoid action. Primary adrenal failure and selected congenital-adrenal-hyperplasia replacement protocols. Not an anti-allergy corticosteroid; monitor BP, oedema and potassium. 5. Route is a safety decision: localise treatment whenever possible Route Clinical use Technique/safety essentials Inhaled Controller therapy for asthma; selected COPD regimens. Not a rescue bronchodilator. Check inhaler technique/adherence, rinse mouth or use spacer where appropriate to reduce thrush/dysphonia, and consider systemic effects at high dose or with CYP3A4 inhibitors. Intranasal Allergic rhinitis, nasal polyps and persistent nasal inflammation. Often more effective

Anti-allergic Agents Antihistaminics: block histamine effects, but choose the receptor, generation and clinical target correctly “Antihistamine” usually means an H1-receptor antagonist/inverse agonist used for allergic symptoms such as itching, urticaria and allergic rhinitis. These medicines relieve histamine-mediated symptoms but do not stop mast-cell degranulation, do not remove an allergen, and do not replace intramuscular adrenaline in anaphylaxis. H2 blockers are a different class, used mainly to reduce gastric acid—not routine allergy medicine. Good prescribing means matching receptor blockade to the diagnosis while preventing sedation, antimuscarinic toxicity, interactions and unsafe self-medication. Do not miss anaphylaxis Airway swelling, wheeze/stridor, collapse, persistent hypotension or rapidly progressive multisystem allergic symptoms require immediate emergency assessment and intramuscular adrenaline according to protocol. H1 antihistamines treat itch/hives but act too slowly and do not reverse life-threatening airway obstruction or shock. Never delay adrenaline for an antihistamine. Lesson map 1. HistamineSynthesis, storage, release and receptor actions. 2. H1 drugsFirst versus second generation, individual medicines and clinical selection. 3. H2 drugsAcid suppression, individual agents and their distinctive risks. 4. ApplicationRhinitis, urticaria, motion sickness, itch, nausea and emergency allergy. 5. SafetySedation, anticholinergic effects, interactions, children, pregnancy and overdose. 6. RevisionCases, exam traps and OSCE counselling. 1. Histamine: where it comes from and why it matters Histamine is an endogenous amine formed from the amino acid histidine by histidine decarboxylase. It is stored preformed in granules, particularly in tissue mast cells (skin, airway and gastrointestinal tract) and circulating basophils. It is also a neurotransmitter in the CNS and has roles in gastric enterochromaffin-like/parietal-cell signalling. How histamine is released Examples Clinical implication IgE-mediated immediate hypersensitivity Allergen cross-links IgE bound to mast-cell/basophil Fcε receptors. Classic urticaria, allergic rhinitis, allergic conjunctivitis and anaphylaxis; histamine is only one of several mediators. Non-IgE mast-cell activation Some drugs, physical stimuli, infections and other direct triggers. Do not label every histamine-mediated reaction as a true IgE allergy without clinical assessment. Cell injury/immune inflammation Tissue inflammation and mast-cell activation in skin/airway/gut. H1 drugs are useful when histamine drives symptoms; they are often insufficient for complex inflammatory disease. The immediate “triple response” of histamine Redness: arteriolar vasodilation. Flare: axon-reflex-mediated surrounding vasodilation. Wheal: increased post-capillary venular permeability causes oedema. H1 antihistamines suppress this wheal-and-flare response, which is a useful pharmacological demonstration but not the entire allergic cascade. 2. Histamine receptors: the map that prevents confusion Receptor Important location / signalling Major effects of histamine Clinical drug relevance H1 Endothelium, smooth muscle, sensory nerves, heart and CNS; predominantly Gq. Itch, sensory-nerve stimulation; bronchial/gut smooth-muscle contraction; vasodilation via NO; increased vascular permeability; wakefulness/vestibular signalling. H1 antihistamines for urticaria, rhinitis, itch, allergy symptoms; selected older drugs for motion sickness/nausea/short-term sedation. H2 Gastric parietal cells, heart, vascular smooth muscle; Gs. Increases gastric acid secretion; contributes to cardiac stimulation and vasodilation. H2 receptor antagonists reduce acid secretion in selected dyspepsia/ulcer/GERD-related indications. They are not a substitute for H1 treatment of allergy. H3 Predominantly presynaptic CNS receptor; Gi. Autoreceptor/heteroreceptor that reduces release of histamine and other neurotransmitters; influences arousal. Not a routine bedside anti-allergy target. Specialist H3-directed therapy exists in limited indications in some settings. H4 Immune cells including eosinophils, mast cells, dendritic cells and T cells. Immune-cell chemotaxis and inflammatory signalling. Research target; no routine standard H4 antagonist for everyday allergic prescribing. 3. How H1 antihistamines work—and what they cannot do Most H1 antihistamines are better described as inverse agonists: they stabilise the inactive receptor state and reduce constitutive H1 activity, while also competitively opposing histamine. They are most effective before or early in histamine-driven symptoms. They do not neutralise histamine already released, block leukotrienes or prostaglandins, prevent mast-cell degranulation, or cure the underlying sensitisation. Why an antihistamine cannot be the sole treatment for anaphylaxis Anaphylaxis is not “just histamine.” It involves airway oedema, bronchospasm, vasodilation, capillary leak and shock from multiple mediators. Adrenaline provides rapid α- and β-adrenergic support; an H1 antihistamine may relieve persistent skin symptoms later but cannot restore perfusion or reliably relieve severe bronchospasm/laryngeal oedema. 4. H1 antihistamines: first generation versus second generation Feature First generation (“sedating”) Second generation (“less sedating”) CNS penetration Cross blood–brain barrier readily; central H1 blockade. Lower CNS penetration because of polarity/P-glycoprotein transport; sedation is lower, not impossible. Receptor selectivity Often non-selective: antimuscarinic, α-blocking and sometimes serotonergic actions. More peripheral H1 selectivity with fewer off-target actions. Duration Often shorter, commonly several daily doses; exceptions exist. Usually longer acting—often once daily—supporting adherence. Adverse-effect pattern Drowsiness, impaired reaction time, confusion/delirium in older people, dry mouth, blurred vision, constipation and urinary retention. Headache, dry mouth/fatigue or occasional drowsiness; much less antimuscarinic burden. Cetirizine/levocetirizine can still sedate some patients. Best role Selected motion sickness, short-term nausea/vertigo, selected itch or short-term night use when sedation is deliberately acceptable. Preferred routine choice for allergic rhinitis and chronic urticaria because daytime function is preserved better. First-generation H1 groups and examples from the supplied lecture EthanolaminesDiphenhydramine, dimenhydrinate. Prominent sedation and antimuscarinic effect; useful in selected motion-sickness/nausea settings, but unsafe before driving. AlkylaminesChlorphenamine (chlorpheniramine), pheniramine. Often less sedating than some older agents but still impair alertness and have antimuscarinic effects. PiperazinesHydroxyzine, cyclizine. Hydroxyzine is sedating and its metabolite includes cetirizine; cyclizine is used for nausea/vertigo in appropriate settings. PhenothiazinesPromethazine. Marked sedation and antimuscarinic action; used selectively for allergy/nausea, with major caution in children and respiratory/CNS depression. PiperidinesCyproheptadine. H1 blockade plus antiserotonergic/antimuscarinic actions; specialist/selected uses, not a routine first-choice non-sedating allergy medicine. Other older agentsCinnarizine is used in some settings for vertigo/motion sickness; it is sedating and has additional pharmacology. Second-generation H1 drugs Drug High-yield pharmacology and use Key safety/selection point Cetirizine Active carboxylated metabolite of hydroxyzine; rapid peripheral H1 effect and common once-daily use for allergic rhinitis/urticaria. Classed less sedating, but sleepiness is common enough to matter. Assess driving/work-at-height response individually; adjust/avoid as appropriate in renal impairment. Levocetirizine Active enantiomer of cetirizine; used for rhinitis/urticaria. Still may cause somnolence; do not assume “newer” means risk-free. Loratadine Long-acting, minimally sedating piperidine; metabolised to active desloratadine. Review hepatic function and interaction risk; appropriate for many daytime allergy presentations. Desloratadine Active metabolite of loratadine; peripheral H1 blocker. Long acting

Anti-Inflammatory Agents Steroidal anti-inflammatory drugs (SAIDs): powerful control of inflammation, never casual prescribing In routine clinical use, SAIDs are mainly glucocorticoids (corticosteroids). They suppress inflammation, allergy and immune activity at many levels, and can be life-saving in selected diseases. The same broad action produces important harms: infection, hyperglycaemia, psychiatric disturbance, hypertension, fluid retention, peptic complications, osteoporosis, cataract/glaucoma, growth suppression and hypothalamic–pituitary–adrenal (HPA) axis suppression. The clinical skill is to use the right steroid, route, dose and duration for a defined indication—and to plan monitoring and stopping before prescribing. Three rules that prevent avoidable harm Do not use systemic steroids merely because a patient has “inflammation.” Define the diagnosis, rule out or treat infection, and use disease-specific treatment where available. Use the lowest effective dose for the shortest period, preferably as a single morning dose when clinically suitable. Local/topical/inhaled treatment may reduce systemic exposure. Never stop prolonged systemic therapy abruptly. Ask about current/recent steroid exposure, give a clear taper/steroid-emergency plan where indicated, and teach the patient when to seek urgent help. Lesson map 1. FoundationsAdrenal physiology, cortisol and HPA axis. 2. MechanismIntracellular receptors, gene regulation, mediator suppression. 3. MedicinesPotency, duration, routes and individual agents. 4. UsesReplacement, anti-inflammatory, anti-allergic and immunosuppressive roles. 5. SafetyInfection, metabolic, bone, eye, neuropsychiatric and adrenal risks. 6. PracticeSelection, monitoring, tapering, cases and OSCE points. 1. What are SAIDs, corticosteroids and glucocorticoids? Corticosteroids are steroid hormones made by the adrenal cortex or manufactured as analogues. They include glucocorticoids (principally cortisol-like metabolic, anti-inflammatory and immunoregulatory actions) and mineralocorticoids (aldosterone-like sodium-retaining, potassium-losing actions). SAIDs in pharmacology teaching usually means glucocorticoid medicines used to suppress inflammation. They are not the same as anabolic-androgenic steroids used for muscle building. Natural glucocorticoids: hydrocortisone (the pharmaceutical form of cortisol) and cortisone. Synthetic drugs: prednisolone/prednisone, methylprednisolone, triamcinolone, dexamethasone and betamethasone. Replacement therapy replaces missing cortisol in adrenal insufficiency. Pharmacological therapy uses larger anti-inflammatory/immunosuppressive exposure for another disease. These are different purposes with different risks and stopping rules. 2. Cortisol physiology and the HPA axis: why withdrawal can be dangerous The hypothalamus releases CRH, stimulating pituitary ACTH; ACTH stimulates the adrenal cortex (zona fasciculata) to produce cortisol. Cortisol normally follows a circadian rhythm—highest in the early morning and lowest around midnight—and rises during severe illness, trauma and surgery. It exerts negative feedback on CRH and ACTH. Physiological action of cortisol Useful survival purpose What excessive pharmacological exposure produces Raises glucose availability through gluconeogenesis and reduced peripheral glucose use Supplies fuel during stress Hyperglycaemia, unmasking/worsening diabetes, increased insulin requirement Mobilises amino acids and inhibits protein formation in some tissues Substrate for acute stress response Muscle wasting/weakness, thin skin, bruising, poor wound healing and bone loss Changes fat mobilisation and deposition Energy redistribution Central/truncal adiposity, moon facies and dorsocervical fat pad Modulates immune and inflammatory reactions Prevents an excessive inflammatory response Infection risk and muted fever/inflammatory signs Some mineralocorticoid activity (especially hydrocortisone) Supports vascular responsiveness and salt-water balance Oedema, hypertension, hypokalaemia and heart-failure worsening HPA-axis suppression Exogenous systemic glucocorticoid tells the brain that enough cortisol is present. CRH/ACTH fall, endogenous cortisol production is suppressed and the adrenal glands may atrophy. Abrupt withdrawal after clinically significant exposure can leave the patient unable to mount a cortisol response to illness: glucocorticoid-induced adrenal insufficiency. Its features include profound fatigue, nausea/vomiting, abdominal pain, dizziness/postural hypotension, hypoglycaemia and, in severe stress, shock. This is why the duration, dose, route, timing and recent courses must be documented. 3. Mechanism of anti-inflammatory and immunosuppressive action Glucocorticoids are lipid soluble and enter cells. They bind a cytosolic glucocorticoid receptor; the activated receptor complex moves into the nucleus and alters transcription. Effects develop over hours because many are genomic, although faster non-genomic effects also occur. Mechanism Key molecular consequence Clinical result Transactivation Increases transcription of anti-inflammatory proteins such as annexin A1 (lipocortin-1), MAPK phosphatase and anti-inflammatory mediators. Annexin A1 inhibits phospholipase A2, reducing arachidonic-acid release and therefore both prostaglandins and leukotrienes. Transrepression Interferes with transcription factors such as NF-κB and AP-1; reduces cytokine/chemokine, COX-2, adhesion-molecule and inflammatory-enzyme expression. Less IL-1, IL-6, TNF and other inflammatory signalling; less leukocyte recruitment and activation. Cellular effects Reduced macrophage/antigen-presenting cell function, lymphocyte redistribution/apoptosis, reduced eosinophils and reduced capillary permeability. Rapid reduction in swelling, itch, wheeze and autoimmune tissue injury—but less immune defence. Membrane/vascular effects Reduced lysosomal enzyme release and inflammatory exudation; increased vascular response to catecholamines. Less oedema and tissue damage; useful adjunct in selected shock states, never a substitute for cause-specific resuscitation. Compare with NSAIDs: NSAIDs mainly inhibit cyclo-oxygenase and prostaglandin formation. Glucocorticoids work upstream at phospholipase A2 and down-regulate COX-2/cytokine genes; therefore they suppress many more inflammatory pathways, including leukotrienes. That greater breadth explains both their power and their wider toxicity. Neither class eradicates an infection or replaces definitive treatment of a surgical problem. 4. Classification: duration, anti-inflammatory potency and mineralocorticoid effect Exact equivalent doses and preparations vary by product and indication. Learn relative potency and duration; use an approved local formulary for dose conversion. Group Examples High-yield clinical meaning Short acting (about 8–12 h) Hydrocortisone, cortisone More mineralocorticoid activity; hydrocortisone is central to adrenal replacement and emergency adrenal-crisis protocols. Intermediate acting (about 12–36 h) Prednisone, prednisolone, methylprednisolone, triamcinolone Common systemic anti-inflammatory agents. Prednisone is converted in the liver to prednisolone; consider this in significant hepatic dysfunction. Long acting (about 36–72 h) Dexamethasone, betamethasone Very potent glucocorticoid activity with minimal mineralocorticoid effect; longer biological action increases HPA-suppression concern. Predominantly local preparations Beclometasone, budesonide, fluticasone, mometasone; topical hydrocortisone/betamethasone/clobetasol; ocular and nasal forms Designed to act at airway, skin, nose, eye, gut or joint. Systemic absorption still matters with high dose, prolonged use, damaged skin, occlusion or interacting medicines. Individual medicine profiles HydrocortisoneCortisol analogue with meaningful mineralocorticoid activity. Used in adrenal replacement and urgent stress/adrenal-crisis pathways; can cause salt-water retention at pharmacological doses. Prednisolone / prednisoneCommon oral systemic anti-inflammatory agents. Prednisone requires hepatic activation to prednisolone. Morning dosing is often preferred when appropriate. MethylprednisoloneIntermediate acting with less mineralocorticoid action than hydrocortisone; used orally or intravenously in selected inflammatory exacerbations and pulse regimens. DexamethasonePotent, long acting and little mineralocorticoid effect. Used