Theophylline and verapamil: Clinically significant drug interaction

Objective: To report and describe a case of verapamil interacting with theophylline. Case Summary: A 33-year-old white man with bronchial asthma was admitted for evaluation of sudden onset of chest pain. During hospitalization, verapamil 120 mg/d was added to the theophylline regimen (600 mg bid). The patient's requirement for theophylline decreased by 50% after the initiation of verapamil. Discussion: A review of the literature indicated that concomitant verapamil may reduce theophylline clearance by 12- 23%. Other reports suggest that the degree of this interaction is of much smaller magnitude and clinically insignificant. Conclusions: Although the most recent FDA labeling guidelines for theophylline mention verapamil as a documented source of drug interaction with theophylline, many clinicians may not realize the potential clinical significance. Therefore, theophylline concentrations should be monitored in patients receiving both theophylline and verapamil, even in the absence of adverse effects.