Lack of effect of food on the pharmacokinetics of an extended-release oxybutynin formulation

The effect of food on the pharmacokinetics of 15 mg oxybutynin XL was evalu ated in a single-dose, randomized, crossover, open-label study in healthy v olunteers. A validated, stereospecific, high-performance liquid chromatogra phy assay was used to simultaneously determine the plasma concentrations of R- and S-oxybutynin and active metabolite R- and S-desethyloxybutynin. The mean AUC and C-max values for each of the four analytes in the fed treatme nt were within +/- 20% of the fasting treatment values. The 90% confidence intervals for the treatment ratios (fed/fasted) for log-transformed C-max a nd AUC(inf) values for the drug isomers and AUC(inf) values for the metabol ite isomers were all within the 80% to 125% range. Only the ranges for the C-max values for R- and S-desethyloxybutynin were slightly wider but were w ell within the 70% to 143% criteria recommended for C-max when comparing ef fect of food. Lack of effect of food on oxybutynin XL is consistent with th e previous observation that the osmotically controlled formulations are nea rly insensitive to the gastrointestinal environment, including food. Oxybut ynin XL was well tolerated, and the safety results were comparable whether administered alone or with food. In conclusion, oxybutynin XL administratio n does not require any caution to be exercised regarding food. (C) 2001 the American College of Clinical Pharmacology.