Which antianginal drug is contraindicated in patients taking phosphodiesterase-5 inhibitors due to risk of severe, refractory hypotension?

Explanation

## Nitrates and Phosphodiesterase-5 Inhibitors: Absolute Contraindication **Key Point:** Organic nitrates (isosorbide dinitrate, isosorbide mononitrate, nitroglycerin) are **absolutely contraindicated** in patients using phosphodiesterase-5 (PDE-5) inhibitors (sildenafil, tadalafil, vardenafil) due to synergistic vasodilation and life-threatening hypotension. ### Mechanism of Dangerous Interaction ```mermaid flowchart TD A[Nitrate: NO release]:::action --> B[↑ cGMP in vascular smooth muscle]:::outcome C[PDE-5 inhibitor: blocks cGMP breakdown]:::action --> B B --> D[Profound vasodilation]:::urgent D --> E[Severe, refractory hypotension]:::urgent E --> F[Syncope, MI, stroke, death]:::urgent ``` ### Pathophysiology 1. **Nitrates** → increase NO → activate guanylate cyclase → ↑ cGMP 2. **PDE-5 inhibitors** → block phosphodiesterase-5 → prevent cGMP breakdown → ↑ cGMP further 3. **Result** — synergistic, unopposed vasodilation with hypotension refractory to vasopressors **Warning:** This is a **black-box warning** in most countries. Even a single dose of a PDE-5 inhibitor within 24 hours (48 hours for tadalafil, which is longer-acting) is dangerous. ### Clinical Management **High-Yield:** Patients with angina and erectile dysfunction should: - Use **alternative ED agents** (e.g., alprostadil, vacuum devices) if nitrates are essential - OR discontinue nitrates and use **non-nitrate antianginals** (calcium channel blockers, beta-blockers, ranolazine, ivabradine) if PDE-5 inhibitors are required ## Comparison: Safety Profile of Antianginals with PDE-5 Inhibitors | Drug | PDE-5 Inhibitor Safe? | Reason | | --- | --- | --- | | **Isosorbide mononitrate** | **NO** | Synergistic vasodilation → severe hypotension | | **Amlodipine** | Yes | Different mechanism; additive but manageable hypotension | | **Atenolol** | Yes | Beta-blocker; no synergistic vasodilation | | **Trimetazidine** | Yes | Metabolic agent; no vasodilatory effect | **Clinical Pearl:** If a patient on nitrates requires ED treatment, discuss this explicitly — many patients do not volunteer this information, leading to dangerous drug interactions.