Which antihypertensive drug class is contraindicated in patients with bilateral renal artery stenosis?

Explanation

## ACE Inhibitors/ARBs in Renal Artery Stenosis **Key Point:** ACE inhibitors and ARBs are contraindicated in bilateral renal artery stenosis (RAS) because they cause acute renal failure by reducing glomerular filtration pressure. ## Mechanism of Renal Injury in Bilateral RAS ```mermaid flowchart TD A[Bilateral renal artery stenosis]:::outcome --> B[Reduced renal perfusion pressure]:::outcome B --> C[Compensatory angiotensin II production]:::outcome C --> D[Efferent arteriole vasoconstriction]:::outcome D --> E[Maintains glomerular filtration pressure]:::outcome F[ACE-I or ARB given]:::action --> G[Block angiotensin II formation/action]:::action G --> H[Loss of efferent vasoconstriction]:::urgent H --> I[Acute drop in GFR]:::urgent H --> J[Acute renal failure]:::urgent ``` **High-Yield:** In bilateral RAS, angiotensin II is essential for maintaining glomerular filtration pressure. Blocking it causes: - Acute rise in serum creatinine (>30% within 1 week) - Hyperkalemia - Acute kidney injury **Warning:** Unilateral RAS is NOT an absolute contraindication; ACE-I/ARB can be used cautiously with monitoring. Bilateral RAS is the critical contraindication. ## Safe Alternatives in Bilateral RAS | Drug Class | Safety in Bilateral RAS | | --- | --- | | Calcium channel blockers | Safe; no effect on efferent arteriole | | Thiazide diuretics | Safe; can be used | | Alpha-2 agonists | Safe; direct vasodilation | | Direct vasodilators | Safe; systemic vasodilation | | ACE-I / ARB | **CONTRAINDICATED** | **Clinical Pearl:** Screen for RAS in patients with sudden onset hypertension, hypertension refractory to 3+ drugs, or acute renal failure after starting ACE-I/ARB.