Formulation and Pharmacokinetic Evaluation of
Controlled-Release Oxybutynin Tablets in Dogs
Abstract
Purpose: To develop and optimize controlled-release (CR) oxybutynin chloride matrix tablets.
Methods: Oxybutynin CR tablets were prepared by embedding drug-containing granules into a
hydrogel matrix of hydroxypropyl methylcellulose (HPMC). A coating layer was then applied with a
mixture of HPMC, ethylcellulose, shellac, and HPMC phthalate. The effect of several formulation
variables on in vitro drug release was studied; furthermore, the drug release kinetics of the optimized
formulation was evaluated. The in vivo pharmacokinetics of the optimized formulation was compared
with those of commercial immediate-release and CR tablets in dogs.
Results: The core tablets exhibited extended release consisting of drug release from the embedded
granules through the erodible hydrogel matrix. Release rate was controlled by the amounts of swellingcontrol
agent and hydrogel used. The optimized formulation followed zero-order release up to 24 h after
an initial lag time. Maximum plasma drug concentration for the optimized and commercial CR tablets
was 5.90 ± 1.42 and 6.47 ± 3.73 ng/mL, respectively, while the area under the plasma concentration–
time curve was 101.40 ± 51.41 and 112.68 ± 65.89 ng∙h/mL, respectively.
Conclusion: The formulated oxybutynin CR tablets exhibit prolonged drug release, thus rendering it a
potentially suitable once-daily oral formulation for improved patient compliance.