Drug interactions between diltiazem and Eryc

GENERALLY AVOID: Coadministration with potent inhibitors of CYP450 3A4 may increase the plasma concentrations of erythromycin, which is primarily metabolized by the isoenzyme. The use of erythromycin has been associated with dose-related prolongation of the QT interval, thus elevated plasma levels of the drug may potentiate the risk of ventricular arrhythmias such as ventricular tachycardia and torsade de pointes. In a population-based retrospective study of 1476 cases of confirmed sudden death from cardiac causes, concurrent use of erythromycin and a CYP450 3A4 inhibitor (mostly verapamil or diltiazem) was associated with a marked increase in the risk of sudden death from cardiac causes as compared to nonuse of CYP450 3A4 inhibitors, erythromycin, or amoxicillin; concurrent use of amoxicillin and CYP450 3A4 inhibitors; use of CYP450 3A4 inhibitors without erythromycin or amoxicillin; and concurrent use of erythromycin and calcium channel blockers that do not significantly inhibit CYP450 3A4 (e.g., nifedipine). In fact, the risk was five times as high as that for nonuse of CYP450 3A4 inhibitors, erythromycin, or amoxicillin. MANAGEMENT: The concurrent use of erythromycin and potent inhibitors of CYP450 3A4 (e.g., itraconazole, ketoconazole, voriconazole, nefazodone, delavirdine, protease inhibitors, ketolide and certain macrolide antibiotics) should be avoided.