The influence of verapamil on theophylline serum concentrations

The effect of verapamil on steady state levels of theophylline were studied in 10 healthy volunteers. Sustained release theophylline 3 mg/kg/day was administered 3 days prior to, and during a 7 day treatment of verapamil 80 mg three times daily. Steady state theophylline levels were measured before giving verapamil and on days 3, 5, and 7 of verapamil. Blood for theophylline assay was drawn one hour before the morning theophylline dose. The results showed no statistically significant difference in theophylline levels before and after verapamil. We conclude that oral verapamil does not affect the disposition of oral theophylline at the dose studied.