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Pharmacokinetics, metabolism, and saliva output during transdermal and extended-release oral oxybutynin administration in healthy subjects.

Author(s): Appell RA, Chancellor MB, Zobrist RH, Thomas H, Sanders SW

Affiliation(s): Department of Urology, Baylor College of Medicine, Houston, Tex 77030, USA. rappell@bcm.tmc.edu

Publication date & source: 2003-06, Mayo Clin Proc., 78(6):696-702.

Publication type: Clinical Trial; Randomized Controlled Trial

OBJECTIVE: To compare the pharmacokinetics and adverse effect dynamics of 2 modified-release oxybutynin treatments. SUBJECTS AND METHODS: Between October 15 and November 6, 2001, 13 healthy subjects (7 men and 6 women) participated in a randomized, 2-way crossover study of transdermal (Oxytrol, 3.9 mg/d) and extended-release oral (Ditropan XL, 10 mg) oxybutynin. Multiple blood and saliva samples were collected. Pharmacokinetic parameters and total salivary output were assessed. Statistical analyses included 95% confidence intervals, paired t test, analysis of variance, and linear regression. RESULTS: Steady-state plasma concentrations were achieved after the first transdermal application and after the second extended-release oral dose. Mean +/- SD 24-hour oxybutynin areas under the concentration-time curve were comparable during transdermal and oral extended-release treatments, 10.8 +/- 24 vs 9.2 +/- 33 ng x h(-1) x mL(-1), respectively. However, the ratio of area under the curve (N-desethyloxybutynin/oxybutynin) after transdermal administration (1.2 +/- 03) was significantly lower (P < .001) than after extended-release oral administration (4.1 +/- 0.9). Mean plasma concentrations were less variable during transdermal compared with extended-release oral administration. Mean +/- SD saliva output was greater during transdermal than extended-release oral treatment (15.7 +/- 93 vs 12.2 +/- 6.8 g, respectively; P = .02). Lower N-desethyloxybutynin during transdermal application was associated with greater saliva output (r = -059, P = .04). No clinically important treatment-related adverse effects were observed. CONCLUSIONS: Transdermal oxybutynin administration results in greater systemic availability and minimizes metabolism to N-desethyloxybutynin compared with extended-release oral administration. Lower N-desethyloxybutynin plasma concentration and greater saliva output during transdermal treatment correspond to the reported low incidence of dry mouth in patients with overactive bladder.

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