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Am Fam Physician. 1999;60(5):1513-1517

Oxybutynin has been used for years in the treatment of urinary incontinence. This medication has been effective in reducing the frequency and total number of incontinent episodes. One of the most common anti-cholinergic side effects of immediate-release oxybutynin is dry mouth, which is one of the main reasons patients stop taking this medication. Anderson and colleagues studied the efficacy and safety of the new controlled-release oxybutynin compared with the immediate-release formula.

A multicenter, randomized, double-blind, parallel group study was conducted at 13 study centers. Patients with a history of urge incontinence or mixed incontinence with a primary urge component who experienced at least six urge incontinent episodes per week when not taking medications were eligible to participate in the study. Of the 158 patients screened, 105 were enrolled. Participants were randomized at each study site into one of two double-line treatment groups. One group received controlled-released oxybutynin starting at a dosage of 5 mg per day and titrated upward to a maximum dosage of 30 mg per day. The other group received the immediate-release formula at a dosage of 5 mg, one to four times per day. All patients were titrated to maximum dosage as it related to their response to urge incontinence or until significant side effects were noted. Patient diaries indicating the number of weekly urge episodes served as the efficacy component for both regimens. The safety of the therapeutic regimens was evaluated with clinical chemistry panels, hematologic tests, urinalysis and electrocardiograms that were performed at the time of screening and at completion of the study. Orthostatic vital signs were measured at baseline, before and after each in-clinic dose of the study drug and at the end of the study. Adverse events were recorded during the patient evaluations.

The discontinuation rate was similar in both groups; only a few were related to adverse side effects. The mean number of weekly urge incontinent episodes, the total number of incontinent episodes and the percentage of reduction in weekly urge incontinent episodes were similarly reduced by the controlled-release and immediate-release oxybutynin. Fewer side effects occurred in the controlled-release group compared with the immediate-release group. The major difference between the two groups was in the number of patients who complained of moderate to severe dry-mouth symptoms.

Controlled- and immediate-release oxybutynin were effective in treating urge incontinence. Continence was obtained across the entire dosage range; therefore, patients should be individualized for this therapeutic regimen. Dosages over 20 mg per day of the controlled-release oxybutynin did not dramatically increase the effectiveness of this medication; thus, higher dosages are not necessary for the majority of patients.

The authors conclude that controlled- and immediate-release oxybutynin were effective in treating urge urinary incontinence. The controlled-release formula produced less dry-mouth side effects.

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