THE PHARMACOKINETICS OF OXYBUTYNIN IS UNAFFECTED BY GENDER AND CONTRACEPTIVE STEROIDS

Objective and methods: The effect of gender and concomitant use of con traceptive steroids on the absorption and metabolism of oxybutynin was investigated in 49 healthy volunteers, 24 females and 25 males. Serum concentrations of oxybutynin and its active metabolite, N-desethyloxy butynin, were measured for up to 48 h after ingestion of a single dose of 10 mg oxybutynin. Results: Intake of oral contraceptive steroids h ad no significant effect on the pharmacokinetic parameters of oxybutyn in or its metabolite. Both in males and females, the mean area under t he curve (AUC(O-t)) of N-desethyloxybutynin was about 13 times higher and the peak concentration (C-max) 15 to 19 times higher than the AUC( O-t) and C-max of the parent oxybutynin, with no significant differenc es between males and females. Conclusions: The pharmacokinetics of ora lly administered oxybutynin shows a considerable interindividual varia bility, but is unaffected by gender and use of contraceptive steroids.