A pharmacogenomics study reveals that poor metabolizers of CYP2D6 who receive a standard dose of metoprolol are most likely to experience which adverse effect due to elevated plasma drug levels?

• A Tachycardia and hypertension
• B Bradycardia and AV block ✓
• C Bronchodilation and hyperglycemia
• D Dry mouth and urinary retention

Explanation

Metoprolol is primarily metabolized by CYP2D6. Poor metabolizers (approximately 7–10% of Caucasians, less common in Asians) have higher plasma metoprolol concentrations after standard doses, leading to exaggerated beta-1 blockade — clinically manifesting as bradycardia and AV block. Tachycardia and hypertension are the opposite effects. Bronchodilation and hyperglycemia would represent beta-2 agonism, not beta blockade. Dry mouth and urinary retention are anticholinergic effects unrelated to metoprolol.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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