PH5.2 | PH5.2 | Cough Pharmacotherapy — SDL Guide — Summary & Reflection

KEY TAKEAWAYS

Cough Pharmacotherapy — Key Points

The fundamental rule: The cough type (dry vs productive) is the decision branch that determines pharmacotherapy. Antitussives for dry cough; expectorants/mucolytics for productive cough. Antitussives in productive cough = harm.

Antitussives:
- Opioid (central): codeine (CYP2D6 pro-drug → morphine; contraindicated <12y, breastfeeding, ultra-rapid metabolisers), pholcodine
- Non-opioid (central): dextromethorphan (NMDA antagonist; contraindicated with MAOIs — serotonin syndrome; caution with SSRIs), noscapine (no dependence/analgesic risk)
- Peripheral: benzonatate (local anaesthetic on vagal afferents), levodropropizine (peripheral opioid-like receptor; no CNS effects)

Expectorants: guaifenesin (preferred OTC; safe in pregnancy), ammonium chloride (avoid in renal disease), potassium iodide (avoid in thyroid disease)

Mucolytics: NAC (cleaves disulfide bonds; also paracetamol antidote), bromhexine/ambroxol (mucokinetic; ambroxol stimulates surfactant), carbocisteine, erdosteine (prodrug)

Drug interactions to remember: DXM + MAOI = absolute contraindication (serotonin syndrome); codeine + CYP2D6 inhibitors (fluoxetine/paroxetine) = reduced efficacy; codeine + CYP2D6 ultra-rapid genotype = toxicity risk

Special populations: Children <12y → no codeine (honey + demulcents instead); Pregnancy → DXM (2nd/3rd trimester) or guaifenesin preferred; Elderly → prefer peripheral antitussives

Always: treat the underlying cause first (ACE-I cough → switch to ARB; GERD cough → PPI; post-nasal drip → INCS; asthma cough → inhaled corticosteroid). Adequate hydration is co-prescribed with every mucolytic.

REFLECT

A 28-year-old breastfeeding mother presents with 4 days of dry, irritating cough after a mild URTI. She mentions she also takes fluoxetine for postpartum depression and cannot sleep due to the cough. Looking back over this module, identify which antitussives are contraindicated in this specific patient and explain the pharmacological mechanism for each contraindication. Then select the most appropriate antitussive for her — or argue for a non-pharmacological approach — and justify your reasoning with reference to the drug's mechanism and safety profile in her situation.