QTc prolongation with concurrent use of azithromycin and diltiazem in an old female patient: a case report

Azithromycin is widely prescribed for the treatment of respiratory tract infections. Incidence of corrected QT interval (QTc) prolongation and cardiac arrest has not been reported after concomitant administration of azithromycin and diltiazem. Here we present a 69-year-old female patient who developed profound QTc prolongation and cardiac arrest after three days of concomitant administration of azithromycin and diltiazem. The patient was successfully resuscitated, intravenous magnesium was given and azithromycin therapy was discontinued. The QTc interval dropped to 412 ms 24 hours after azithromycin discontinuation. One week later, the patient was discharged home after full recovery. This case illustrates a possible drug interaction between azithromycin and P-glycoprotein inhibitor drugs and/or drugs having an effect on cardiac repolarization.