Oxybutynin gel shows comparable efficacy as patch, fewer side effects

A once-daily oxybutynin topical gel for overactive bladder exhibited steady-state pharmacokinetics similar to that of the oxybutynin patch (Oxytrol) in a study presented at the AUA annual meeting. The presentation reviewed comparative data between the currently marketed patch and a 10% w/w ethanolic gel, which is nearing commercial availability.

"I would expect that, based on the comparative serum levels of oxybutynin and desethyloxybutynin, the gel formulation will preserve many of the advantages associated with the transdermal patch," said David Staskin, MD, of Weill-Cornell Medical College, New York.

"However, the gel should minimize the irritative side effects on the skin attributed to the patch, which include hyper-hydration from skin occlusion, abrasion from adhesive removal, and irritation from chemical component effects."

Dr. Staskin added that while the patch has proven to be clinically effective and systemically tolerable, skin reactions such as pruritis, erythema, and rash or macules are associated with its use.

Twenty-two male and female volunteers, ages 18 to 44, took part in the randomized, open-label, two-way, crossover study. Subjects received 18 days of gel therapy (1 gram four times daily) or one patch every 3.5 days for 2 weeks, followed by a 4-day application (3.9 mg/day). Participants then received the crossover formulation after a 14-day washout period.

Serum levels of oxybutynin and the active metabolite desethyloxybutynin were obtained during the final 4 days of dosing to measure drug concentrations. Those levels turned out to be very similar between the gel and the patch throughout the 4 days, with mean oxybutynin levels approximately 2.9% higher for the gel than for the patch.

Erythema was not reported at any application site of the gel, no serious or severe adverse events were reported, and no patient discontinued because of an adverse event, Dr. Staskin said.

Dr. Staskin serves as an adviser to Watson Pharmaceuticals and Antares Pharma.