Treatment of asthma
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I now have comprehensive, well-sourced content from multiple authoritative textbooks. Here is a thorough synthesis:
Treatment of Asthma
Overview
Asthma management is built on two pillars: relievers (bronchodilators for acute symptoms) and controllers (anti-inflammatory agents for long-term control). Treatment is adjusted in a stepwise fashion guided by GINA (Global Initiative for Asthma) and NHLBI-EPR guidelines, with the goal of minimising daily symptoms and exacerbation risk while using the least medication necessary. — Murray & Nadel's Textbook of Respiratory Medicine
Pharmacological Mechanism Overview
Drug Classes
1. β₂-Adrenoceptor Agonists (Bronchodilators)
The cornerstone of asthma therapy. They bind β₂ receptors on airway smooth muscle → activate adenylyl cyclase → ↑ cAMP → smooth muscle relaxation. They also reduce mast cell mediator release and vascular permeability. — Katzung's Basic and Clinical Pharmacology, 16th Ed.
Short-Acting β₂ Agonists (SABAs) — Rescue therapy
- Albuterol (salbutamol) — most widely used; onset within 15 min, duration 3–4 h
- Delivered by MDI (100–400 mcg) or nebuliser (2.5–5 mg)
- Used for symptom relief and before exercise
- Overuse (>2 doses/week) signals inadequate control → step-up needed
Long-Acting β₂ Agonists (LABAs) — Add-on controller (never monotherapy)
- Salmeterol, formoterol, indacaterol — duration 12–24 h
- Always combined with an ICS; salmeterol monotherapy was associated with increased asthma-related death
- Formoterol has a faster onset and can be used as both controller and reliever (MART strategy)
Adverse effects: tachycardia, tremor, hypokalaemia (dose-related, mostly with systemic/high-dose inhaled use)
2. Inhaled Corticosteroids (ICS) — Primary Controllers
The most effective anti-inflammatory agents for persistent asthma. They reduce airway hyperresponsiveness, decrease exacerbation frequency, and are the first-line controller at all GINA steps 2–5.
| Drug | Common doses |
|---|---|
| Budesonide | 200–800 mcg/day |
| Fluticasone propionate | 100–500 mcg/day |
| Beclomethasone | 100–400 mcg/day |
| Mometasone | 200–400 mcg/day |
Adverse effects: oral candidiasis, dysphonia (local); with high doses — adrenal suppression, reduced bone density (systemic)
Always use a spacer and rinse mouth after use to reduce oropharyngeal deposition.
3. ICS + LABA Combinations
Adding a LABA to an ICS improves symptom control and reduces exacerbations more than doubling the ICS dose. Examples:
- Budesonide/formoterol (can be used as MART — Maintenance And Reliever Therapy)
- Fluticasone/salmeterol
- Fluticasone furoate/vilanterol (once daily)
4. Muscarinic Antagonists (Anticholinergics)
Block M3 receptors on airway smooth muscle → reduce cholinergic bronchoconstriction.
Short-acting (SAMA): Ipratropium bromide
- Onset ~15–30 min, duration ~4–6 h
- Particularly useful in acute severe asthma in the ED (combined with SABA)
- Dose in acute exacerbation: 0.5 mg nebulised every 20 min × 3, then as needed
Long-acting (LAMA): Tiotropium
- Add-on therapy at GINA step 4–5 for adults with poorly controlled asthma
- Reduces exacerbation risk as an adjunct to ICS ± LABA
5. Methylxanthines (Theophylline)
Mechanism: Inhibits phosphodiesterase (PDE) → ↑ cAMP; also antagonises adenosine receptors. Moderate bronchodilator with mild anti-inflammatory effects.
- Narrow therapeutic index: serum levels must be monitored (target 5–15 mcg/mL)
- Use has declined due to availability of safer, more effective agents
- Still used as add-on in severe asthma in resource-limited settings
Adverse effects (dose-related): nausea, vomiting, insomnia, seizures, arrhythmias
6. Leukotriene Receptor Antagonists (LTRAs)
- Montelukast, zafirlukast — block cysteinyl leukotriene (CysLT₁) receptors
- Oral agents; useful for mild persistent asthma, aspirin-sensitive asthma, and exercise-induced bronchoconstriction
- Less effective than ICS as monotherapy; can be used as ICS add-on
- Note: Montelukast carries an FDA black-box warning for neuropsychiatric effects (depression, suicidal ideation)
7. Biologic/Targeted Therapies (GINA Step 5 — Severe Asthma)
For patients with uncontrolled severe asthma despite high-dose ICS + LABA:
| Drug | Target | Indication |
|---|---|---|
| Omalizumab | Anti-IgE | Allergic asthma, elevated serum IgE |
| Mepolizumab, reslizumab | Anti-IL-5 | Eosinophilic asthma |
| Benralizumab | Anti-IL-5Rα | Eosinophilic asthma |
| Dupilumab | Anti-IL-4Rα (blocks IL-4 + IL-13) | Type 2 asthma, also treats atopic dermatitis |
| Tezepelumab | Anti-TSLP | Broad severe asthma (any phenotype) |
8. Systemic Corticosteroids
- Reserved for acute exacerbations and severe persistent asthma not controlled by inhaled therapy
- Oral prednisolone 40–50 mg/day for 5–7 days in acute exacerbations
- Chronic oral steroids: associated with significant adverse effects (osteoporosis, diabetes, immunosuppression, adrenal suppression); minimise where possible
GINA Stepwise Management (Adults)
| Step | Treatment |
|---|---|
| Step 1 (Mild intermittent) | As-needed low-dose ICS-formoterol (preferred) OR as-needed SABA alone |
| Step 2 (Mild persistent) | Low-dose ICS daily + as-needed SABA; or as-needed ICS-formoterol |
| Step 3 (Moderate persistent) | Low-dose ICS-LABA + as-needed SABA/ICS-formoterol; or medium-dose ICS |
| Step 4 (Moderate-severe) | Medium/high-dose ICS-LABA ± tiotropium + as-needed reliever |
| Step 5 (Severe uncontrolled) | Add biologic therapy (omalizumab, anti-IL-5, dupilumab, tezepelumab); consider low-dose oral corticosteroid |
Step-up when asthma is uncontrolled; step-down when well controlled for ≥3 months. — Murray & Nadel's Textbook of Respiratory Medicine
Classification of control (GINA):
- Well controlled: 0 of 4 criteria (no daytime symptoms >2×/week, no night waking, no activity limitation, reliever ≤2×/week)
- Partly controlled: 1–2 criteria
- Uncontrolled: 3–4 criteria
Inhaler Device Selection
Inhaled therapy is the cornerstone of asthma treatment — it delivers drug directly to the lung, requires smaller doses, has faster onset, and fewer systemic effects than oral therapy. — Fishman's Pulmonary Diseases and Disorders
| Device | Advantages | Disadvantages |
|---|---|---|
| pMDI | Portable, inexpensive, multidose | Requires hand-breath coordination; high oropharyngeal deposition |
| DPI | Breath-actuated (no coordination needed) | Requires adequate inspiratory flow |
| Nebuliser | Useful for acute/severe patients; tidal breathing | Bulky, time-consuming |
Key point: Always teach and check inhaler technique. Poor technique is a major cause of treatment failure.
Management of Acute Exacerbations (Emergency Department)
Source: Tintinalli's Emergency Medicine
Goals: rapid reversal of airflow obstruction, adequate oxygenation, reduction of inflammation.
Initial treatment (Mild–Moderate, FEV₁/PEFR ≥40%):
- Oxygen to maintain SaO₂ ≥90%
- Inhaled SABA (albuterol) via nebuliser or MDI+spacer, up to 3 doses in first hour
- Oral systemic corticosteroids if no immediate response
Severe (FEV₁/PEFR <40%):
- Oxygen
- High-dose inhaled SABA + ipratropium by nebulisation every 20 min or continuously for 1 hour
- Oral/IV systemic corticosteroids
Impending respiratory arrest:
- Intubation + mechanical ventilation with 100% oxygen
- Nebulised SABA + ipratropium
- IV corticosteroids
Albuterol dosing (acute):
- Nebuliser: 2.5–5 mg every 20 min × 3 doses, then 2.5–10 mg every 1–4 h as needed; or 10–15 mg/h continuous nebulisation
- Ipratropium: 0.5 mg every 20 min × 3 doses
Discharge criteria (Good response): FEV₁/PEFR ≥70%, sustained 60 min after last treatment, no distress. Discharge with: continued SABA, oral corticosteroid course, ICS initiation, follow-up in 1–4 weeks.
Non-Pharmacological Measures
- Allergen and trigger avoidance (house dust mite, pollen, pet dander, occupational exposures, smoke, NSAIDs in aspirin-sensitive asthma, β-blockers)
- Written Asthma Action Plan — patients use PEFR and symptoms to self-manage
- Smoking cessation
- Weight loss in obese patients (improves control significantly)
- Breathing exercises (Buteyko, diaphragmatic) — adjunct; reduce symptom perception
- Allergen immunotherapy — subcutaneous or sublingual; modifies disease in allergic asthma
Recent Evidence (2024–2025)
A 2025 JAMA network meta-analysis (PMID: 39465893) compared inhaled reliever therapies and found that ICS-formoterol used as-needed reliever was associated with better outcomes than SABA alone, supporting the GINA recommendation for ICS-containing relievers even in mild asthma.
Key sources: Katzung's Basic and Clinical Pharmacology, 16th Ed. · Murray & Nadel's Textbook of Respiratory Medicine · Fishman's Pulmonary Diseases and Disorders · Tintinalli's Emergency Medicine
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