title: Compound cardiac toxicity of oral erythromycin and verapamil.
abstract: OBJECTIVE
  To report a case of complete atrioventricular (AV) block and QTc prolongation following coadministration of high-dose verapamil and erythromycin.
  
  
  METHODS
  A 79-year-old white woman was admitted to the hospital due to extreme fatigue and dizziness. On admission, heart rate was 40 beats/min and blood pressure was 80/40 mm Hg. An electrocardiogram showed complete atrioventricular (AV) block, escape rhythm of 50 beats/min, and QTc prolongation 583 msec. This event was attributed to concomitant treatment with verapamil 480 mg/d and erythromycin 2,000 mg/d, which was prescribed one week before admission.
  
  
  CONCLUSIONS
  This is the first case published describing complete AV block and prolongation of QTc following coadministration of erythromycin and verapamil. CYP3A4 is the main isoenzyme responsible for metabolism of erythromycin and verapamil. Both drugs are potent inhibitors of CYP3A4 and of P-glycoprotein; this may be the basis for the pharmacokinetic interaction between erythromycin and verapamil. In addition to being a woman, our patient had other risk factors for QT prolongation: slow baseline heart rate (probably induced by verapamil), left-ventricular hypertrophy, and possibly ischemic heart disease.
  
  
  CONCLUSIONS
  This life-threatening arrhythmia was probably the result of a pharmacokinetic and/or pharmacodynamic interaction of high-dose verapamil and erythromycin.
authors.affiliation: Department of Medicine, Hadassah University Hospital, Ein Kerem, Jerusalem, Israel.
authors.forename: N
authors.initials: N
authors.lastname: Goldschmidt
authors.forename: T
authors.initials: T
authors.lastname: Azaz-Livshits
authors.lastname: Gotsman
authors.forename: R
authors.initials: R
authors.lastname: Nir-Paz
authors.forename: A
authors.initials: A
authors.lastname: Ben-Yehuda
authors.forename: M
authors.initials: M
authors.lastname: Muszkat
mesh_terms: D000368:Aged; D000900:Anti-Bacterial Agents / Q000009:adverse effects*; D001772:Blood Cell Count; D002121:Calcium Channel Blockers / Q000009:adverse effects*; D004562:Electrocardiography / Q000187:drug effects; D004917:Erythromycin / Q000009:adverse effects*; D005260:Female; D006327:Heart Block / Q000139:chemically induced*; D006801:Humans; D008133:Long QT Syndrome / Q000139:chemically induced*; D014700:Verapamil / Q000009:adverse effects*
chemical_list: D000900:Anti-Bacterial Agents; D002121:Calcium Channel Blockers; D004917:Erythromycin; D014700:Verapamil