Erythromycin prolongs the QTc interval among patients with pneumonia

Erythromycin is commonly used to treat simple community-acquired pneumonia. We measured the prolongation in QT(c) intervals in EKGs associated with intravenous erythromycin administration among patients hospitalized for simple pneumonia (DRGs 89 and 90). We reviewed the medical records of 50 patients who received at least 5 days of intravenous erythromycin, and found 15 with readable paired EKGs, at least one taken during the period of erythromycin administration and at least one other obtained when the patient had no erythromycin. The mean QT(c) interval in lead II for EKGs taken without erythromycin was 0.422 s and the average prolongation of the QT(c) interval associated with erythromycin administration was 0.046 s (P<0.01). The administration of erythromycin was thus associated with an increase in QT(c) intervals to a mean of 0.468 s, a value considered to be abnormally prolonged. We conclude that erythromycin prolongs the QT(c) interval among patients hospitalized with pneumonia in the same manner previously reported for healthy volunteers in an experimental setting. The magnitude of this erythromycin-induced QT(c) prolongation raises QT(c) intervals into the abnormal range. Although no patient in this small study suffered an adverse effect from the QT(c) prolongation, the magnitude of this effect is sufficiently large to raise clinical concerns.