A 52-year-old man with hypertension and angina is started on a beta blocker. Which of the following is the most common adverse effect that limits the use of beta blockers in clinical practice?

Explanation

## Most Common Adverse Effect of Beta Blockers **Key Point:** Fatigue and sexual dysfunction (erectile dysfunction) are the most common dose-limiting adverse effects of beta blockers in routine clinical practice, affecting 10–20% of patients on therapy. ### Why Fatigue Occurs 1. Reduced cardiac output due to decreased heart rate and contractility 2. Decreased cerebral blood flow 3. Reduced metabolic rate 4. CNS penetration (especially lipophilic agents like propranolol) ### Why Sexual Dysfunction Occurs 1. Reduced penile blood flow (β₂-mediated vasodilation is blocked) 2. Decreased sympathetic outflow required for ejaculation 3. Psychological effects from fatigue and depression 4. More common with non-selective beta blockers ### Frequency Comparison of Adverse Effects | Adverse Effect | Frequency | Severity | Clinical Impact | |---|---|---|---| | Fatigue & sexual dysfunction | 10–20% | Mild–moderate | Most common reason for discontinuation | | Bronchospasm | 2–5% | Severe | Only in asthmatics/COPD; absolute contraindication | | Hypokalemia | Rare | Mild | Occurs with thiazides, not beta blockers alone | | Tachycardia | Rare | Mild | Occurs on withdrawal, not during therapy | **Clinical Pearl:** Sexual dysfunction is often underreported by patients; clinicians must specifically ask. Switching to a cardioselective beta blocker (e.g., atenolol, bisoprolol) or adding a vasodilator may improve symptoms. **High-Yield:** Fatigue is the reason most patients stop beta blockers voluntarily; it is NOT a sign of overdose but rather a dose-related effect that may improve with time or dose reduction. ### Why Other Options Are Less Common - **Bronchospasm:** Occurs only in 2–5% of patients with underlying airway disease; is a contraindication, not a common adverse effect in the general population. - **Hypokalemia:** Beta blockers actually cause mild *hyperkalemia* (via reduced aldosterone secretion), not hypokalemia. - **Tachycardia:** Occurs on *withdrawal* (rebound tachycardia), not during therapy; during therapy, heart rate decreases. [cite:KD Tripathi 8e Ch 12]