A 62-year-old man with hypertension on enalapril for 3 months develops a persistent dry cough and mild dyspnea. He denies fever, chest pain, or orthopnea. Chest X-ray is normal. His blood pressure is well-controlled at 128/82 mmHg. What is the most appropriate next step in management?

Explanation

## Clinical Context This patient presents with a classic **Type A (Augmented) Adverse Drug Reaction** — a dose-dependent, predictable side effect of ACE inhibitors caused by accumulation of bradykinin and substance P in the lungs. ## Mechanism of ACE Inhibitor-Induced Cough **Key Point:** ACE inhibitors block conversion of angiotensin I to angiotensin II AND inhibit degradation of bradykinin and substance P. These inflammatory mediators accumulate in respiratory epithelium, triggering a dry, persistent cough in 5–10% of patients. ## Diagnostic Features - Onset: typically 1–3 months after initiation (as in this case) - Character: dry, non-productive, worse at night or when lying down - Investigations: normal chest X-ray, normal spirometry (rules out organic lung disease) - Resolution: occurs within 1–4 weeks of drug discontinuation ## Management Algorithm ```mermaid flowchart TD A[ACE inhibitor-induced cough suspected]:::outcome --> B{Diagnosis confirmed?}:::decision B -->|Yes: normal CXR, typical timeline| C[Discontinue ACE inhibitor]:::action C --> D[Switch to ARB or alternative agent]:::action B -->|No: abnormal CXR, fever, crackles| E[Investigate for pneumonia, ILD]:::urgent D --> F[Cough resolves in 1-4 weeks]:::outcome ``` **High-Yield:** ARBs (losartan, valsartan) do NOT cause cough because they block the angiotensin II receptor downstream and do not affect bradykinin metabolism. They are the preferred alternative in ACE inhibitor-induced cough. ## Why Discontinuation + ARB Switch? 1. **Diagnosis is Type A (predictable, dose-related)** — not a rare idiosyncratic reaction 2. **Normal CXR excludes organic pathology** — no need for advanced imaging 3. **ARBs provide equivalent BP control without cough** — evidence-based alternative 4. **Cough suppressants are ineffective** — they do not address the underlying mechanism **Clinical Pearl:** Some patients tolerate cough and choose to continue ACE inhibitors; however, switching to an ARB is the standard recommendation when cough is bothersome or affects quality of life. [cite:KD Tripathi 8e Ch 26]