Obstructive lung disease questions love to hide the diagnosis in the med list. If you can instantly recognize which inhaler class does what, you’ll pick up easy points on Step 1/2 (and avoid classic traps like “LABA monotherapy in asthma”). Below is a quick-hit, shareable comparison table with a simple visual mnemonic and the highest-yield facts.
The “ABCD” Inhaler Map (visual mnemonic)
Think of obstructive inhalers as ABCD:
- A = β2 Agonists (open airways fast; “A for Air”)
- B = muscarinic Blockers (dry up bronchoconstriction/secretions)
- C = Corticosteroids (calm inflammation; asthma-heavy)
- D = other Drugs (leukotriene modifiers, PDE inhibitors, biologics)
One-liner anchor: A & B bronchodilate; C prevents asthma flares; D is add-ons for specific phenotypes.
Comparison Table: Inhaler Classes (high-yield)
| Class | Common drugs (USMLE favorites in bold) | Mechanism (one-liner) | Onset / role | Biggest Step-relevant adverse effects | Board-style pearls / traps |
|---|---|---|---|---|---|
| SABA | Albuterol, levalbuterol | cAMP in bronchial smooth muscle bronchodilation | Rescue (minutes) for acute bronchospasm | Tremor, tachycardia/palpitations, hypokalemia | Frequent use suggests poor control → needs controller (often ICS). Can cause mild lactic acidosis in high-dose acute tx. |
| LABA | Salmeterol, formoterol | Same as SABA, longer action | Maintenance (esp. COPD; asthma only with ICS) | Same as SABA | Never LABA monotherapy in asthma (↑ asthma-related death). Formoterol has faster onset vs salmeterol (still not “rescue-only” in classic teaching). |
| SAMA | Ipratropium | Muscarinic (M3) blockade → bronchodilation + ↓ secretions | COPD maintenance; adjunct in acute exacerbations (esp. with SABA) | Dry mouth, urinary retention; minimal systemic effects | Great in COPD; also used acutely with albuterol for COPD/asthma exacerbation. |
| LAMA | Tiotropium, umeclidinium, aclidinium | Longer M3 blockade | COPD maintenance (first-line long-acting bronchodilator) | Anticholinergic effects; caution in BPH/glaucoma | In COPD: LAMA often beats LABA for exacerbation reduction. Can be add-on in some asthma regimens. |
| ICS | Budesonide, fluticasone, beclomethasone | Local anti-inflammatory: ↓ eosinophils/cytokines | Controller (asthma core therapy) | Oropharyngeal candidiasis, dysphonia; systemic at high dose | Rinse mouth to prevent thrush. In COPD: use for frequent exacerbations/eosinophilic phenotype; ↑ pneumonia risk. Not for acute relief. |
| ICS/LABA combo | Budesonide-formoterol, fluticasone-salmeterol | Anti-inflammatory + long bronchodilation | Maintenance; reduces exacerbations | Same as both | Fixes the “LABA monotherapy” trap. Many step stems hint “on combination inhaler” → think moderate-persistent asthma/COPD with exacerbations. |
| Systemic steroids (not inhaler, but tested with inhalers) | Prednisone, methylprednisolone | Broad anti-inflammatory | Acute exacerbations (asthma/COPD) | Hyperglycemia, mood changes, hypertension, immunosuppression | Acute severe asthma: SABA + ipratropium + systemic steroids ± Mg. Don’t forget “recent steroid burst” in history. |
| Leukotriene receptor antagonist (LTRA) | Montelukast, zafirlukast | Blocks CysLT1 → ↓ bronchoconstriction/mucus | Add-on controller; allergic rhinitis, aspirin-exacerbated resp disease | Neuropsychiatric effects (montelukast), rare hepatotoxicity | Great when asthma + allergic rhinitis. Aspirin-induced asthma: leukotriene pathway involvement. Not a rescue med. |
| 5-LO inhibitor (oral) | Zileuton | ↓ leukotriene synthesis | Less common controller | Hepatotoxicity | Boards love distinguishing from montelukast: zileuton hits synthesis; monitor LFTs. |
| PDE-4 inhibitor (oral) | Roflumilast | ↑ cAMP in inflammatory cells → ↓ neutrophilic inflammation | Severe COPD/chronic bronchitis w frequent exacerbations | Weight loss, insomnia, anxiety/depression | Think: “COPD frequent exacerbations despite inhalers” → roflumilast add-on. |
| Methylxanthine (rare) | Theophylline | PDE inhibition + adenosine antagonism → bronchodilation | Rare due to narrow TI | Arrhythmias, seizures; many drug interactions | If tested, it’s usually toxicity: nausea → arrhythmia/seizure; CYP interactions. |
| Mast cell stabilizer | Cromolyn | Prevents mast cell degranulation | Prophylaxis pre-exposure/exercise (rare now) | Cough, throat irritation | Old-school but Step likes mechanism: “stabilizes mast cells.” Not for acute attacks. |
| Biologics (injectable; Step 2/3 more) | Omalizumab (anti-IgE), mepolizumab/benralizumab (anti-IL-5), dupilumab (anti-IL-4R) | Target allergic/eosinophilic pathways | Severe persistent asthma phenotypes | Injection reactions; anaphylaxis (omalizumab) | Clues: high IgE/allergies → omalizumab. High eosinophils/nasal polyps → anti-IL-5 or dupilumab. Not “inhalers,” but show up in refractory asthma stems. |
Fast “Which disease gets which inhaler?” cheat sheet
Asthma (especially Step 1 classic)
- Rescue: SABA (albuterol)
- Controller foundation: ICS
- Add-on: LABA only with ICS (ICS/LABA combo)
- Special situations:
- Exercise-induced: SABA pre-exercise (and/or controller if frequent)
- Aspirin-exacerbated: consider montelukast (leukotrienes)
COPD (Step 2 loves management + exacerbations)
- Maintenance bronchodilators: LAMA or LABA (often both)
- Add ICS if frequent exacerbations / eosinophilic features (but remember pneumonia risk)
- Exacerbation: SABA ± SAMA + systemic steroids (and antibiotics if indicated)
One-liner memory hooks (ultra-shareable)
- Albuterol = “A” for Acute bronchospasm relief.
- Salmeterol = “S” for Scheduled (not solo in asthma).
- Ipratropium = “I” for Inhibits vagal bronchoconstriction (COPD friend).
- Tiotropium = “T” for Takes time (long-acting COPD maintenance).
- ICS = Inflammation Control in asthma, not instant relief.
- Montelukast = “Monty blocks Leukotrienes” → good for allergic rhinitis + asthma.
USMLE high-yield pitfalls (don’t miss these)
- LABA monotherapy is contraindicated in asthma → always pair with ICS.
- ICS adverse effects are local: thrush + hoarseness → “rinse mouth” counseling.
- COPD first-line maintenance is bronchodilation (LAMA/LABA); ICS is selective add-on (exacerbations/eosinophils).
- Antimuscarinics can worsen urinary retention (BPH) and angle-closure glaucoma symptoms.
- SABA overuse is a red flag: indicates uncontrolled asthma and higher exacerbation risk.