Oxybutynin

Placebo-controlled studies

Oxybutynin 15 mg/day has been compared with a newer anticholinergic agent, tolterodine 4 mg/day, in a randomized, double-blind, placebo-controlled parallel group study in 293 patients with bladder detrusor instability [ ]. The efficacies were generally similar, but twice as many patients taking oxybutynin withdrew because of adverse reactions (17% versus 8%). Dry mouth was by far the most frequent adverse reaction, reported by 86% of patients taking oxybutynin and 50% of those taking tolterodine. Although there was still an excess of adverse reactions after halving the dose of oxybutynin, it would not be normal practice to start treatment with this drug in a dosage as high as 15 mg/day.