Bronchodilators: complete pharmacology and clinical use
Bronchodilators relax airway smooth muscle and increase airway calibre. They reduce bronchoconstriction, improve expiratory flow and relieve wheeze, chest tightness and work of breathing. They do not all treat the same pathology: beta2-agonists rapidly reverse smooth-muscle contraction; antimuscarinics reduce vagally mediated bronchoconstriction; methylxanthines have a narrow therapeutic window and are now generally second-line. Asthma also contains airway inflammation, so a bronchodilator should not replace anti-inflammatory controller therapy.
Learning objectives
- Explain airway smooth-muscle tone and the receptor pathways targeted by bronchodilators.
- Classify short- and long-acting beta2-agonists, antimuscarinics and methylxanthines.
- Describe individual drugs, formulations, doses, indications, contraindications, adverse effects, interactions and monitoring.
- Choose appropriate bronchodilator therapy in acute asthma, COPD exacerbation, chronic asthma, chronic COPD and exercise-induced bronchoconstriction.
- Recognise toxicity, inhaler errors, paradoxical bronchospasm and situations requiring urgent escalation.
Airway physiology and the pharmacological target
Airway diameter is influenced by parasympathetic cholinergic tone, circulating catecholamines, inflammatory mediators, airway smooth-muscle calcium and the amount of mucus or oedema. Bronchodilators mainly relax smooth muscle; they cannot remove a mucus plug, reverse fixed fibrosis or treat alveolar fluid. The clinical response should therefore be assessed objectively with respiratory rate, work of breathing, oxygen saturation, peak expiratory flow where appropriate, chest auscultation and mental state.
| Pathway | What happens | Drug response |
|---|---|---|
| Beta2-adrenoceptor stimulation | Gs protein activates adenylyl cyclase, raising cAMP; protein kinase A reduces myosin light-chain phosphorylation and relaxes bronchial smooth muscle. | Rapid bronchodilation; also improves mucociliary clearance and may inhibit mediator release. |
| Muscarinic M3 stimulation | Acetylcholine from vagal nerves activates Gq/IP3 pathways, causing bronchoconstriction and mucus secretion. | Antimuscarinics block this pathway and are especially useful in COPD. |
| Phosphodiesterase inhibition/adenosine antagonism | Methylxanthines increase intracellular cyclic nucleotides and antagonise adenosine effects. | Bronchodilation, but systemic toxicity limits routine use. |
Classification of bronchodilators
Short-acting beta2-agonists (SABA)
Salbutamol/albuterol and terbutaline. Rapid onset; used for acute bronchospasm and pre-exercise prevention.
Long-acting beta2-agonists (LABA)
Salmeterol and formoterol; ultra-long agents include indacaterol, olodaterol and vilanterol. Maintenance therapy, not routine acute rescue.
Antimuscarinics
Ipratropium is short-acting; tiotropium, umeclidinium, glycopyrronium and aclidinium are long-acting maintenance agents.
Methylxanthines
Theophylline and aminophylline. Oral or IV use requires caution, interaction review and serum-level monitoring.
Combination therapy
SABA plus ipratropium for severe acute obstruction; LABA/LAMA and ICS/LABA/LAMA combinations for chronic obstructive disease.
1. Beta2-adrenergic agonists
Beta2-agonists bind airway beta2 receptors and increase cAMP. Inhaled delivery produces a higher airway concentration with fewer systemic effects than oral or parenteral therapy. Selectivity is relative, not absolute: at high doses, beta1 cardiac stimulation and peripheral vascular effects become clinically important.
Short-acting beta2-agonists
| Drug/formulation | Common teaching dose | Uses | Important adverse effects |
|---|---|---|---|
| Salbutamol/albuterol MDI | Adults and children ≥4 years: 2 puffs (100 micrograms/puff) every 4–6 h as needed. Use a spacer when possible. | Acute bronchospasm, asthma symptom relief, prevention of exercise-induced bronchospasm. | Tremor, tachycardia, palpitations, nervousness, headache, hypokalaemia, hyperglycaemia and lactic acidosis at high repeated doses. |
| Salbutamol nebuliser | Adult acute severe bronchospasm: commonly 2.5–5 mg nebulised, repeated according to response/protocol. Children often receive 2.5 mg; severe attacks may require 5 mg, weight and guideline dependent. | Severe asthma/COPD exacerbation when inhaler technique or respiratory distress limits MDI use. | Monitor heart rate, potassium, lactate, oxygenation and response. Do not delay systemic corticosteroids or escalation. |
| Terbutaline | Inhaled doses vary by device; a commonly taught dry-powder dose is 0.5 mg when required, subject to product maximum. SC/IV use is specialist emergency practice. | Alternative SABA where available; bronchospasm and exercise prevention. | Similar beta-agonist effects; systemic route causes more tremor, tachycardia and hypokalaemia. |
Repeated SABA in acute asthma
In a severe attack, repeated inhaled salbutamol is often delivered by oxygen-driven nebuliser or repeated puffs through a spacer. Give oxygen to the target range recommended by the local asthma guideline, add ipratropium for severe/life-threatening attacks, administer systemic corticosteroids early and reassess after each treatment cycle. A “silent chest,” exhaustion, cyanosis, confusion, rising carbon dioxide or inability to speak indicates impending respiratory failure; bronchodilator repetition must not delay senior airway and critical-care help.
Long-acting beta2-agonists
| Drug | Common maintenance dose | Clinical place | Safety rule |
|---|---|---|---|
| Salmeterol | 50 micrograms inhaled twice daily, approximately 12 h apart; follow device instructions. | Long-term asthma or COPD maintenance; slower onset than formoterol. | Not a rescue medicine. In asthma, use with an inhaled corticosteroid; never use LABA monotherapy. |
| Formoterol | Often 12 micrograms inhaled twice daily in maintenance products. In ICS-formoterol regimens, reliever and maintenance dosing are product- and guideline-specific. | Asthma and COPD maintenance; rapid onset allows selected ICS-formoterol maintenance-and-reliever strategies. | Do not substitute one device or strength for another. Check maximum daily inhalations in the local protocol. |
| Indacaterol/olodaterol/vilanterol | Once-daily inhalation in product-specific strengths. | COPD maintenance; selected combination products. | Not for acute bronchospasm. Review cardiovascular effects and device technique. |
Beta-agonist contraindications and interactions
- Use caution: tachyarrhythmia, ischaemic heart disease, uncontrolled hypertension, hyperthyroidism, diabetes, hypokalaemia and seizure disorders.
- Beta-blockers: non-selective beta-blockers can antagonise bronchodilation and provoke bronchospasm. If a beta-blocker is essential, specialist selection and monitoring are required.
- Diuretics and corticosteroids: combined hypokalaemic effects may be clinically important during repeated nebulised therapy.
- MAO inhibitors/tricyclic antidepressants: can increase cardiovascular effects; review timing and risk.
- Digoxin: hypokalaemia can increase arrhythmia risk.
- Paradoxical bronchospasm: sudden worsening immediately after inhalation requires stopping the preparation and urgent alternative treatment.
2. Antimuscarinic bronchodilators
Acetylcholine released by parasympathetic nerves activates M3 receptors and contracts airway smooth muscle. Antimuscarinics competitively block this response. They are particularly effective in COPD, where cholinergic tone is a major reversible component of airflow limitation.
| Drug | Common dose | Uses and limitations |
|---|---|---|
| Ipratropium MDI | 2 inhalations four times daily; additional inhalations may be allowed by product guidance, but many labels limit total to 12 inhalations/24 h. | COPD maintenance and acute severe asthma as an adjunct to SABA. Slower onset than salbutamol. |
| Ipratropium nebuliser | 500 micrograms by nebuliser three to four times daily in chronic use. In acute severe asthma/COPD, 500 micrograms may be combined with salbutamol and repeated according to local emergency protocol. | Useful when the patient cannot coordinate an inhaler or during severe airflow obstruction. |
| Tiotropium HandiHaler | 18 micrograms inhaled once daily as two inhalations from one capsule; never swallow the capsule and never use more than one dose/24 h. | Long-term COPD maintenance; selected add-on asthma therapy. Not rescue therapy. |
| Tiotropium Respimat | Product strengths differ; commonly two inhalations once daily. | Maintenance bronchospasm control; device-specific dose must be checked. |
| Umeclidinium/glycopyrronium/aclidinium | Usually once- or twice-daily inhalation depending on the product. | Long-acting COPD maintenance, often combined with a LABA. |
Antimuscarinic adverse effects and precautions
- Dry mouth, throat irritation, cough, blurred vision, constipation and urinary retention.
- Caution in narrow-angle glaucoma, prostatic obstruction, urinary retention and severe constipation.
- Avoid spraying into the eyes: mydriasis, eye pain and acute angle-closure glaucoma can occur.
- Allergic reactions and paradoxical bronchospasm are uncommon but require immediate treatment.
- Tiotropium and other LAMAs are maintenance agents; they should not be used to rescue sudden severe breathlessness.
3. Methylxanthines: theophylline and aminophylline
Theophylline inhibits phosphodiesterases and antagonises adenosine receptors, increasing cyclic nucleotide activity and reducing bronchial smooth-muscle contraction. It may improve diaphragmatic contractility and stimulate the respiratory centre, but the therapeutic window is narrow. Aminophylline is a soluble theophylline–ethylenediamine complex used for IV administration in selected settings.
| Preparation | Teaching dose examples | Monitoring |
|---|---|---|
| Modified-release theophylline | Adult doses vary by preparation, smoking status, age and clearance; a common starting range is 200–300 mg twice daily, then individualise. | Measure serum concentration after steady state or dose changes. A usual target range is approximately 5–15 micrograms/mL; toxicity becomes more likely as levels rise, especially above 20. |
| Child oral theophylline | Weight-based dosing only; product examples use approximately 10 mg/kg twice daily or 10–16 mg/kg/day divided, with lower limits in risk groups. | Never copy adult dosing. Monitor serum level, pulse, nausea, sleep, tremor and seizure risk. |
| Aminophylline IV | Specialist protocol only. If no theophylline has been taken recently, a loading dose may be considered; maintenance infusions are weight- and age-based. A commonly taught maintenance range is about 0.5–0.7 mg/kg/h in adults, but local protocol and serum levels govern. | Check prior theophylline exposure, ECG, potassium, glucose and serum concentration. Give slowly; rapid IV administration can cause hypotension and arrhythmia. |
Theophylline toxicity
Early toxicity produces nausea, vomiting, abdominal pain, tremor, agitation, insomnia, headache, tachycardia and palpitations. Severe toxicity causes persistent vomiting, hypokalaemia, hyperglycaemia, hypotension, supraventricular or ventricular arrhythmias, seizures, hyperthermia and death. Obtain serum concentration, ECG, glucose, electrolytes, renal/liver tests and urgent toxicology/critical-care input in suspected overdose.
Theophylline interactions
| Factor/drug | Effect | Clinical action |
|---|---|---|
| Smoking tobacco | Induces clearance; stopping smoking can raise levels. | Reassess dose after smoking cessation or relapse. |
| Macrolides and fluoroquinolones | Some reduce clearance and increase toxicity. | Check interaction before prescribing; monitor level and symptoms. |
| Cimetidine, allopurinol, fluvoxamine and some anticonvulsants | May alter metabolism. | Review the complete medicine list and adjust under supervision. |
| Fever, heart failure and liver disease | Reduce clearance. | Use lower doses and closer therapeutic-drug monitoring. |
| Carbamazepine, phenytoin, rifampicin | May increase clearance and reduce effect. | Do not increase dose reflexively; confirm adherence and serum level. |
4. Combination bronchodilator therapy
Salbutamol + ipratropium
Provides complementary beta2 and antimuscarinic bronchodilation. Used in severe acute asthma and COPD exacerbations; nebulised combination products commonly contain salbutamol 2.5 mg or 3 mg plus ipratropium 0.5 mg in 3 mL, depending on product.
LABA + LAMA
Improves sustained bronchodilation in COPD when one long-acting agent is inadequate. Review inhaler technique and adherence before escalating.
ICS + LABA or triple therapy
In asthma, ICS treats airway inflammation and LABA improves bronchodilation. In COPD, ICS is added for selected exacerbation/eosinophil phenotypes, not automatically for every patient.
Acute asthma: emergency bronchodilator pathway
- Assess severity immediately: speech, respiratory rate, pulse, accessory-muscle use, peak flow, oxygen saturation, mental state and exhaustion.
- Give inhaled SABA: repeated salbutamol by spacer or nebuliser. In children, a common initial nebulised dose is 2.5 mg; severe attacks may require 5 mg according to weight and protocol.
- Add ipratropium in severe/life-threatening attacks: commonly 0.5 mg nebulised with salbutamol, repeated according to local protocol.
- Give corticosteroid early: bronchodilation without anti-inflammatory treatment is incomplete. Use the local oral/IV corticosteroid regimen.
- Oxygen and monitoring: target the local asthma oxygen range; reassess work of breathing, wheeze, peak flow, heart rate, potassium and lactate when treatment is intensive.
- Escalate: poor response, exhaustion, confusion, silent chest, rising carbon dioxide, severe hypoxaemia or respiratory arrest requires senior airway/critical-care management. IV aminophylline is not a routine substitute for repeated inhaled therapy and should only be used by experienced clinicians.
COPD exacerbation: emergency and maintenance principles
Short-acting beta2-agonist with or without short-acting ipratropium is commonly used for acute symptom relief. Evaluate infection, pneumonia, pneumothorax, pulmonary embolism, heart failure, carbon dioxide retention and medication adherence. In chronic COPD, a LAMA or LABA/LAMA combination is usually the bronchodilator foundation. Assess inhaler technique, smoking exposure, vaccinations, pulmonary rehabilitation and exacerbation history.
Inhaler and nebuliser technique
| Device issue | Why it matters | Teaching point |
|---|---|---|
| Pressurised MDI coordination | Actuation without slow inhalation leaves medicine in the mouth. | Exhale, seal lips, press once while inhaling slowly and deeply, hold breath about 10 seconds if able; use a spacer. |
| Dry-powder inhaler | Requires a forceful, deep inhalation; moisture damages powder. | Prepare the dose, exhale away from device, inhale forcefully, hold breath and close/store correctly. |
| Nebuliser | Airflow, mask leak and poor cooperation reduce delivery. | Use the prescribed diluent and dose; monitor pulse, oxygenation and response; do not let nebulisation delay escalation. |
| Mixed devices | Different strengths and schedules cause overdose or undertreatment. | Demonstrate each device and ask the patient to return-demonstrate technique. |
Contraindications, cautions and adverse-effect recognition
- Cardiovascular: tremor and tachycardia are common; new chest pain, syncope, sustained palpitations or arrhythmia requires review.
- Metabolic: repeated beta2 doses may cause hypokalaemia, hyperglycaemia and lactic acidosis. Do not misinterpret rising lactate as treatment failure without reassessment of airflow and perfusion.
- Glaucoma/urinary retention: antimuscarinics can worsen both, especially if aerosol reaches the eyes.
- Pregnancy: do not withhold essential rescue bronchodilation; use guideline-supported inhaled therapy and obstetric review when needed.
- Hyperthyroidism and diabetes: monitor cardiovascular and glucose effects with high-dose systemic exposure.
- Hypersensitivity/paradoxical bronchospasm: stop the culprit preparation and use emergency alternative treatment.
Clinical cases
Case 1: severe asthma with a silent chest
A patient is barely speaking, exhausted and has very little air entry. This is not reassurance from “less wheeze”; it may mean critically reduced airflow. Give immediate SABA plus ipratropium, oxygen and systemic corticosteroids while calling senior airway/critical-care support. Do not rely on oral theophylline or delay escalation.
Case 2: COPD with tachycardia after repeated nebulisers
Assess oxygenation, ECG, potassium, lactate, work of breathing and response. Tachycardia may be drug-related but can also indicate hypoxia, sepsis, arrhythmia or cardiac disease. Continue life-saving therapy while treating the cause and avoid unmonitored repeated doses.
Case 3: theophylline patient prescribed an interacting antibiotic
Check the exact antibiotic, current theophylline formulation, smoking status, liver/heart disease and symptoms. Arrange serum-level monitoring and dose review rather than assuming a previous stable dose remains safe.
High-yield revision points
- Beta2-agonists increase cAMP and rapidly relax airway smooth muscle.
- SABA relieves acute bronchospasm; LABA maintains control and is not routine rescue therapy.
- In asthma, LABA should be paired with inhaled corticosteroid therapy.
- Ipratropium blocks M3-mediated bronchoconstriction and is especially useful in COPD and severe acute asthma as an adjunct.
- Tiotropium is a once-daily maintenance LAMA, not a rescue inhaler.
- Theophylline/aminophylline has a narrow therapeutic window and many interactions; monitor serum concentration.
- Repeated nebulised beta2-agonists can cause tremor, tachycardia, hypokalaemia, hyperglycaemia and lactic acidosis.
- A silent chest, confusion, exhaustion or worsening gas exchange is an emergency even if wheeze decreases.
