Inhibition of theophylline elimination in rabbits by verapamil

Single intravenous dose pharmacokinetics of theophylline in 10 rabbits were investigated before and after 5 days oral administration of verapamil in daily doses of 6 mg/kg. Verapamil caused a significant inhibition of theophylline elimination. Theophylline clearance was reduced from 126 to 98 ml/hr/kg (22.2%) whereas the steady state volume of distribution of the drug increased from 461 to 550 ml/kg (19.3%). The terminal half-life of theophylline increased from 2.7 to 4.0 hr (49.8%).