Clinical rule: diarrhoea kills through dehydration and electrolyte loss. ORS, continued feeding and treatment of the cause come before symptom-stopping drugs. Never use an antimotility drug to keep blood, high fever, invasive organisms or toxic colitis inside the bowel.
Learning objectives
Classify diarrhoea and dehydration; prescribe low-osmolarity ORS and zinc; choose or avoid loperamide and related drugs; recognise invasive disease; use etiology-directed antimicrobials safely; distinguish diarrhoea treatment from IBD treatment; and state adult/paediatric dose limits and danger signs.
1. Diarrhoea and intestinal fluid physiology
Diarrhoea is passage of frequent loose or watery stools. About 8–10 L of fluid enters the gut daily from intake and secretions; almost all is normally reabsorbed. Stool water rises when secretion exceeds absorption, epithelial transport is damaged or intestinal transit is so fast that absorption time falls. The sodium–glucose cotransporter remains functional in most infectious diarrhoeas: glucose-linked sodium uptake pulls water with it—the basis of ORS.
| Type | Mechanism/examples | Clinical implication |
|---|---|---|
| Secretory | Increased chloride/water secretion: cholera, enterotoxigenic E. coli, viral gastroenteritis, drugs | Large watery stool; ORS remains effective |
| Inflammatory/invasive | Mucosal invasion: Shigella, Campylobacter, Salmonella, amoebic colitis, IBD | Blood/mucus, fever, pain; do not use loperamide alone |
| Motility-related | IBS, anxiety, hyperthyroidism, prokinetics | Treat cause; selected symptom relief may be appropriate |
| Osmotic/malabsorptive | Lactose intolerance, laxatives, malabsorption | Stop osmotic trigger and investigate if persistent |
2. Causes: take a cause-focused history
- Infectious: viral gastroenteritis, cholera, travellers’ diarrhoea, enteric fever, protozoa (Giardia, E. histolytica), C. difficile.
- Non-infectious: food/toxins, anxiety/IBS, inflammatory bowel disease, coeliac disease, endocrine disease.
- Drug-induced: antibiotics altering flora; colchicine; metformin; magnesium; laxatives; cholinergic/anticholinesterase drugs; prokinetics.
3. Assessment and emergency triage
Urgent referral/IV management: lethargy/altered consciousness, shock, inability to drink, repeated vomiting, severe dehydration, sunken eyes with poor perfusion, oliguria, bloody diarrhoea with systemic illness, severe abdominal pain/peritonism, high fever, severe malnutrition, infant age, immunosuppression, suspected cholera outbreak or diarrhoea lasting ≥14 days.
Assess onset, stool volume/blood/mucus, vomiting, urine output, thirst, exposures, travel, antibiotics, comorbidities and drugs. Classify hydration and weigh children where possible. Send stool testing when invasive/prolonged/severe disease, outbreak, immunocompromise or treatment failure is suspected.
4. Rehydration is the first anti-diarrheal treatment
4.1 WHO low-osmolarity ORS
One litre contains NaCl 2.6 g, KCl 1.5 g, trisodium citrate dihydrate 2.9 g and glucose anhydrous 13.5 g: sodium 75 mmol/L, glucose 75 mmol/L, potassium 20 mmol/L, chloride 65 mmol/L, citrate 10 mmol/L; total osmolarity 245 mOsm/L. Mix only with the stated volume of safe water—never make a concentrated sachet.
| Situation | Dose/regimen |
|---|---|
| No dehydration (Plan A) | Give ORS after each loose stool: child <2 y 50–100 mL; 2–10 y 100–200 mL; older child/adult as much as wanted. Continue breastfeeding/feeding. |
| Some dehydration (Plan B) | 75 mL/kg ORS over 4 hours, reassess, then replace ongoing losses. |
| Severe dehydration (Plan C) | Urgent IV Ringer’s lactate preferred: 100 mL/kg. Age ≥12 months/adults: 30 mL/kg in 30 min then 70 mL/kg in 2.5 h. Infant <12 months: 30 mL/kg in 1 h then 70 mL/kg in 5 h. Use local protocol and start ORS when able to drink. |
4.2 Nutrition and zinc
Continue age-appropriate feeding and breastfeeding; starvation worsens malnutrition and mucosal recovery. For children with acute diarrhoea: zinc 10 mg orally once daily for 10–14 days if under 6 months; 20 mg once daily for 10–14 days if 6 months or older. Zinc is adjunctive—not a replacement for ORS or assessment.
5. Classification of drug treatment
Antimotility opioids
Loperamide, diphenoxylate; selected short-term symptom control only.
Antisecretory/adsorbent agents
Racecadotril, bismuth subsalicylate; use depends on age/setting.
Cause-directed antimicrobials
Only for defined/strongly suspected bacterial, protozoal or C. difficile disease.
IBD anti-inflammatory therapy
5-ASA and corticosteroids treat inflammation, not ordinary infectious diarrhoea.
6. Antimotility opioids
Mechanism
Opioid agonists act mainly at enteric µ (and some δ) receptors: reduce propulsive peristalsis, increase segmental tone, prolong transit and increase water/electrolyte absorption; they also reduce secretion. This can relieve non-invasive diarrhoea but can dangerously retain pathogens/toxin in dysentery, pseudomembranous colitis or acute severe colitis.
6.1 Loperamide
Loperamide is a peripheral µ-opioid agonist with minimal CNS penetration at therapeutic doses. It is the preferred antimotility drug for suitable adults because it is more potent and has less central effect than codeine or diphenoxylate.
| Patient | Typical dose | Maximum/limit |
|---|---|---|
| Adult acute non-bloody diarrhoea | 4 mg orally once, then 2 mg after each loose stool | OTC maximum 8 mg/day; prescription maximum 16 mg/day. Stop if no improvement by 48 h. |
| Adult chronic diarrhoea/ileostomy | Specialist-directed; commonly 2 mg after loose stool, titrated | Do not exceed 16 mg/day without specialist review; identify cause. |
| Children | Do not use under 2 years. In acute childhood diarrhoea, WHO-based care prioritises ORS/zinc and generally avoids loperamide. | Only use age/weight-specific local paediatric protocol when a clinician has selected it. |
Never give loperamide for bloody/black stool, fever with suspected dysentery, mucus with systemic illness, suspected invasive Salmonella/Shigella/Campylobacter, antibiotic-associated C. difficile colitis, acute ulcerative colitis/toxic megacolon risk, abdominal pain without diarrhoea, ileus/abdominal distension, or age <2 years. Excess doses can cause QT prolongation, torsades, cardiac arrest and death.
6.2 Diphenoxylate + atropine
Diphenoxylate is a synthetic opioid that crosses the blood–brain barrier. Atropine is added in small quantity to discourage misuse; anticholinergic toxicity can occur in overdose.
Adult dose: 5 mg diphenoxylate (usually two 2.5 mg tablets each containing atropine 0.025 mg) orally four times daily initially; maximum 20 mg diphenoxylate/day. Reduce to the lowest effective maintenance dose once control occurs. Do not use in young children; follow the local label. Avoid in infectious/invasive diarrhoea, obstruction, severe colitis and respiratory/CNS-depression risk.
6.3 Codeine
Codeine has central and peripheral opioid effects and dependence/respiratory-depression risk. It is not routine first-line treatment. A historical adult antidiarrhoeal regimen is 30–60 mg orally every 6–8 hours (maximum 240 mg/day), but this must be specialist-led and avoided in children, pregnancy where possible, respiratory disease, opioid use disorder and infectious diarrhoea. The supplied slide’s “no central action” statement is incorrect.
7. Other symptomatic agents
Racecadotril
Racecadotril inhibits enkephalinase, reducing intestinal hypersecretion without slowing transit. It is an adjunct to ORS where licensed/available.
Adult: 100 mg orally three times daily before main meals until two normal stools, usually no more than 7 days. Child: 1.5 mg/kg orally three times daily (product-specific sachet strengths; do not exceed local licensed guidance). Continue ORS.
Bismuth subsalicylate
Provides antisecretory, anti-inflammatory and antimicrobial effects. It can darken tongue/stool harmlessly. Age ≥12/adult: 524 mg (30 mL liquid or 2×262 mg tablets) every 30–60 minutes as needed; maximum 8 doses in 24 h, and no more than 2 days without review. Avoid in aspirin/salicylate allergy, anticoagulation, significant renal disease, ulcer/bleeding risk, pregnancy unless directed, and children/teenagers with viral illness because of Reye-syndrome risk.
Anticholinergics
Atropine/scopolamine reduce gut motility and secretion but have poor benefit in secretory diarrhoea and may worsen retention. They are not routine acute-diarrhoea therapy. If an antispasmodic is considered for IBS-type cramping, use a diagnosis-led, short course and avoid in obstruction, glaucoma, urinary retention and frail older adults.
8. Antimicrobials: use only when indicated
Most acute watery diarrhoeas are self-limited and need ORS, not antibiotics. Culture/resistance and national guidance determine treatment. The lecture lists co-trimoxazole, norfloxacin and tetracycline regimens; resistance patterns and safety have changed, so do not prescribe them empirically from old notes.
| Defined situation | Example adult regimen* | Key principle |
|---|---|---|
| Severe cholera | Azithromycin 1 g orally once OR doxycycline 300 mg orally once | Antibiotic shortens illness; ORS/IV fluids remain lifesaving. Doxycycline avoid in pregnancy/young children. |
| Severe travellers’ diarrhoea/Campylobacter where antibiotic indicated | Azithromycin 1 g once OR 500 mg daily for 3 days | Use local resistance/travel guidance; avoid routine antibiotics in mild illness. |
| Shigellosis/dysentery | Azithromycin 500 mg daily for 3 days or culture-guided alternative | Stool testing/local susceptibility essential; no loperamide alone. |
| C. difficile infection | Vancomycin 125 mg orally four times daily for 10 days or fidaxomicin 200 mg twice daily for 10 days | Stop inciting antibiotic if possible; isolate and follow facility protocol. |
| Giardiasis | Tinidazole 2 g orally once OR metronidazole 400 mg three times daily for 5–7 days | Confirm/strongly suspect diagnosis; manage contacts/water exposure. |
| Invasive amoebiasis | Metronidazole 800 mg three times daily for 5–10 days then luminal agent | Tissue amoebicide alone does not clear luminal cysts; use specialist/local protocol. |
*Typical teaching doses for non-pregnant adults with normal organ function; local Uganda/national guidelines, culture, pregnancy, age, weight and renal/hepatic status override this table.
9. Anti-inflammatory/antisecretory therapy in IBD
Sulfasalazine
Sulfasalazine is 5-aminosalicylic acid linked to sulfapyridine by an azo bond; colonic bacteria release 5-ASA for local anti-inflammatory action. It treats ulcerative colitis/selected colonic Crohn disease—not infectious diarrhoea. Adult induction: 2–4 g/day orally in divided doses; maintenance: 2 g/day divided. Supplement folic acid; monitor full blood count and liver function. Adverse effects include nausea, rash, fever, headache, reversible oligospermia, haemolysis (check G6PD risk), hepatitis, cytopenia and folate deficiency.
Mesalazine (5-ASA)
Mesalazine delivers active 5-ASA to distal ileum/colon in formulation-dependent fashion. Ulcerative-colitis induction: oral 2–4.8 g/day once daily or divided; maintenance: 1.2–2.4 g/day. Rectal formulations use formulation-specific doses. Monitor renal function before and during therapy; adverse effects include headache, abdominal pain, rash, pancreatitis and interstitial nephritis.
Corticosteroids
Prednisolone induces remission in moderate/severe IBD flare but does not maintain remission. A common adult regimen is prednisolone 40 mg orally once daily, then taper according to response/specialist plan. Distal colitis/proctitis may use hydrocortisone rectal preparations (for example 100 mg enema nightly for 2–3 weeks, then taper, product-specific). Exclude infection and involve specialist care.
10. Cases and high-yield recall
Case: child with watery diarrhoea
A 15-month-old has 6 watery stools, drinks eagerly and has no blood. Assess dehydration; give ORS after every stool, continue feeding and give zinc 20 mg daily for 10–14 days. Do not give loperamide.
Case: bloody fever diarrhoea
An adult has fever, cramping and blood/mucus in stool. Rehydrate, test/treat for invasive infection per local guideline and refer if severe. Loperamide is unsafe.
- ORS corrects dehydration; it does not directly stop stool output.
- Loperamide adult: 4 mg once then 2 mg after loose stool; max 8 mg OTC/16 mg prescription per day.
- ORS plus zinc is the key child strategy; zinc: 10 mg <6 months, 20 mg ≥6 months for 10–14 days.
- Antibiotics are selective, not routine; treat cause and follow resistance guidance.
- 5-ASA/steroids treat IBD, not ordinary infectious diarrhoea.
Sources for further study
- Supplied lecture: Antidiarrheals drug (SlideShare).
- WHO: Zinc supplementation in diarrhoea.
- World Gastroenterology Organisation: Acute diarrhoea global guideline.
- DailyMed: Loperamide prescribing information.
