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Verapamil toxicity resulting from a probable interaction with telithromycin.
Matthew Reed1, Geoffrey C Wall, Niyati P Shah
1Iowa Methodist Medical Center, Des Moines, IA, USA.
The Annals of Pharmacotherapy
|December 16, 2004
Summary
Telithromycin may cause verapamil toxicity, leading to severe hypotension and bradycardia. This drug interaction highlights the importance of considering CYP3A4 metabolism when prescribing antibiotics like telithromycin to patients on verapamil.
Area of Science:
- Pharmacology
- Clinical Toxicology
- Drug Interactions
Background:
- Verapamil is a calcium channel blocker commonly prescribed for hypertension.
- Telithromycin is a ketolide antibiotic used for respiratory tract infections.
- Both verapamil and telithromycin interact with the CYP3A4 enzyme system.
Observation:
- A 76-year-old woman on daily verapamil developed severe hypotension and bradycardia after a 2-day course of telithromycin.
- The patient presented with a blood pressure of 50-60 mm Hg and a heart rate of 30 beats/min.
- Symptoms resolved within 72 hours of admission after treatment with fluids, vasopressors, and transvenous pacing.
Findings:
- The patient's symptoms were attributed to verapamil toxicity, likely due to an interaction with telithromycin.
- Telithromycin, a CYP3A4 substrate, may displace verapamil from this metabolic pathway, increasing verapamil levels.
- Other potential causes for the patient's condition were ruled out.
Implications:
- Clinicians should exercise caution when prescribing telithromycin to patients taking verapamil or other drugs metabolized by CYP3A4.
- This case underscores the potential for significant drug interactions with telithromycin.
- Awareness of potential pharmacokinetic interactions is crucial for patient safety.