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Verapamil Toxicity Resulting from a Probable Interaction with Telithromycin

Internal Medicine Resident, Iowa Methodist Medical Center (IMMC), Des Moines, IA

Geoffrey C Wall, PharmD BCPS

Internal Medicine Clinical Pharmacist, IMMC; Assistant Professor of Pharmacy Practice, College of Pharmacy and Health Sciences, Drake University, Des Moines

Niyati P Shah

PharmD Student, College of Pharmacy and Health Sciences, Drake University

James M Heun

Medical Student, College of Medicine, University of Iowa, Iowa City, IA

Gregory A Hicklin, MD FCCM

Staff Pulmonologist, IMMC

Reprints: Dr. Wall, College of Pharmacy and Health Sciences, Drake University, 2507 University Ave., Des Moines, IA 50311-4505, fax 515/241-5085, geoff.wall{at}drake.edu

OBJECTIVE: To report a case of hypotension and bradyarrhythmia caused by verapamil toxicity in a patient prescribed telithromycin.

CASE SUMMARY: A 76-year-old white woman receiving verapamil 180 mg/day for hypertension experienced a sudden onset of shortness of breath and weakness and was found to be profoundly hypotensive and bradycardic, with a systolic blood pressure of 50–60 mm Hg and a heart rate of 30 beats/min. She had been taking telithromycin 800 mg/day for 2 days previously for acute sinusitis. The patient was treated with crystalloids, vasopressors, and transvenous pacing. Approximately 72 hours after admission, her blood pressure and heart rate rapidly returned to normal, and she was discharged several days later.

DISCUSSION: Telithromycin is a known substrate of the CYP3A4 system, and several pharmacokinetic interactions can occur by displacement of other drugs from this system. Verapamil is metabolized through several cytochrome P450 isoenzyme systems. Although there are no previous reports of an interaction between these drugs, other possible causes for the patient's symptoms were excluded and the diagnosis of a probable interaction between verapamil and telithromycin leading to verapamil toxicity was made.

CONCLUSIONS: Telithromycin is a ketolide antibiotic approved for treatment of respiratory tract infections and acute sinusitis. The potential for clinically significant drug interactions should be considered before using this agent, especially in patients taking other drugs that are metabolized through the CYP3A system. Caution should be exercised when considering the use of this antibiotic in patients receiving verapamil.

Key Words: telithromycin, verapamil, interaction

Published Online, December 14, 2004. www.theannals.com, DOI 10.1345/aph.1E496

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