Pharmacokinetic disposition of intravenous and oral pentoxifylline in horses.

The pharmacokinetics of pentoxifylline (P) and its alcohol metabolite I (MI) were determined after administration of intravenous pentoxifylline, sustained release pentoxifylline tablets (Trental), and crushed pentoxifylline tablets in corn syrup, to five healthy adult horses. Pharmacokinetics were evaluated in a model-independent manner. After intravenous administration, pentoxifylline was rapidly eliminated (mean residence time 1.09 +/- 0.67 h), had a large steady-state volume of distribution (2.81 +/- 1.16 l/kg), and high clearance (3.06 +/- 1.05 l/kg/h). Oral absorption of pentoxifylline from both dose forms varied considerably between individuals. Times to peak concentration ranged from 1-10 h for either dose form. There was no difference in relative bioavailability (F') between whole (0.98 +/- 0.30) and crushed Trental tablets. Ratios between areas under the curve (AUC) for pentoxifylline and MI were different following administration of oral versus intravenous doses. This finding suggests that route of administration may affect the metabolic profile of pentoxifylline. Given the extreme differences in absorption characteristics between individuals in this study, recommendations are not made as to appropriate dose, dose interval, or dose form for administration of pentoxifylline to horses.