Pharmacokinetics and Reversible Biotransformation of Sulfinpyrazone and Its Metabolites in Rabbits. II. Multiple-Dose Study.

In crossover studies rabbits were given sulfmpyrazone (SO) and its sulfide metabolite (S) perorally once daily (10 mg/kg) for 5 days. Comparison of the pharmacokinetic parameters obtained after the first and the fifth dose indicates that repeated dosing does not alter disposition kinetics of both SO and S, except that in dosing with S the observed terminal half-life for S is significantly reduced, from 4.59 ± 0.55 to 2.86 ± 0.6 hr (SD). In other studies rabbits were given higher single doses (15, 25, and 50 mg/kg) perorally and comparison was made between these dose sizes and the first dose (10 mg/kg) of multiple administration with S. Some kinetic parameters tended to be altered in a nonlinear fashion, and greater intersubject variations were observed because of the dose increase, while oxidation to SO or p-hydroxylation to OH-S from S was not significantly altered.