Erythromycin QT Prolongation — NDEB AFK MCQ
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Correct answer: C — Terfenadine (and other QT-prolonging drugs)
Erythromycin (and other macrolide antibiotics) inhibits the cytochrome P450 enzyme CYP3A4, which metabolises many drugs. When combined with QT-prolonging drugs (e.g., terfenadine — now withdrawn, cisapride, certain antipsychotics, fluoroquinolones), it can cause dangerous prolongation of the QT interval, predisposing to torsades de pointes (a potentially fatal ventricular arrhythmia). Erythromycin itself also directly prolongs the QT interval. This interaction is clinically important when prescribing macrolides as penicillin alternatives.
Reference: Katzung – Basic and Clinical Pharmacology, 15th ed., 2021