A 58-year-old Indian male with hypertension and type 2 diabetes mellitus is prescribed an ACE inhibitor for renal protection. After 3 weeks, he develops a persistent dry cough and mild facial swelling. On examination, there is no evidence of heart failure or infection. The structure marked **C** in the RAAS diagram is the target of which class of antihypertensive agents that would be most appropriate for this patient?

Explanation

## Why Angiotensin Receptor Blockers (ARBs) is right The structure marked **C** is the Angiotensin II AT1 receptor. ARBs (losartan, valsartan, telmisartan) block this receptor directly, producing the same downstream hemodynamic and renal protective effects as ACE inhibitors. Critically, because ARBs do NOT inhibit ACE, they do NOT cause bradykinin accumulation—the mechanism responsible for the dry cough and angioedema seen with ACE inhibitors. This patient's cough and facial swelling are classic ACE inhibitor adverse effects due to bradykinin buildup. ARBs are the ideal replacement in ACE-inhibitor-intolerant patients, with identical indications for hypertension and diabetic nephroprotection but without the cough or angioedema. (Guyton & Hall 14e Ch 19; KD Tripathi 9e Ch 36) ## Why each distractor is wrong - **Aldosterone antagonists like spironolactone**: While spironolactone blocks the downstream effect of aldosterone (structure **D**), it does not directly target the AT1 receptor (**C**). Additionally, spironolactone causes hyperkalemia and gynecomastia, making it unsuitable as a first-line replacement for this patient's ACE inhibitor intolerance. - **Direct renin inhibitors like aliskiren**: These agents block renin (structure **A**), not the AT1 receptor (**C**). Although they reduce angiotensin II formation, they are not first-line agents and do not address the specific mechanism of ACE inhibitor adverse effects. - **Calcium channel blockers like amlodipine**: These agents work through a completely different mechanism (L-type calcium channel blockade) and do not target the AT1 receptor (**C**). While effective for hypertension, they lack the renal protective effect in diabetic nephropathy that the patient requires. **High-Yield:** ARBs are the drug class of choice for ACE-inhibitor-intolerant patients because they block AT1 receptors without causing bradykinin accumulation—thus avoiding cough and angioedema while maintaining renal protection in diabetes. [cite: Guyton & Hall 14e Ch 19; KD Tripathi 9e Ch 36]