Comparative pharmacokinetics of theophylline and dyphylline following intravenous injection in rabbits.

The pharmacokinetics of theophylline and dyphylline in four rabbits were investigated following intravenous injection. Each rabbit received theophylline (10 mg/kg) first then dyphylline (25 mg/kg) two weeks afterwards as an intravenous bolus injection. The serum concentration-time data for both theophylline and dyphylline were best fitted to the two compartment open model. The half-lives of theophylline and dyphylline were 5.5 +/- 1.3 and 0.74 +/- 0.10 hr, respectively. The apparent volume of distribution (Vdbeta) and total body clearance (TBC) of dyphylline (Vdbeta = 1008 +/- 156 ml/kg; TBC = 942 +/- 118 ML/HR/KG)a = 1008 +/- 156 ml/kg; TBC = 942 +/- 118 ml/hr/kg) were much higher than those of theophylline (Vdbeta = 545 +/- 160 ml/kg; TBC = 69 +/- 10 ml/hr/kg). Thus both theophylline and dyphylline showed pronounced difference in their pharmacokinetic profile.