A randomized controlled trial comparing the efficacy of controlled-release oxybutynin tablets (10 mg once daily) with conventional oxybutynin tablets (5 mg twice daily) in patients whose symptoms were stabilized on 5 mg twice daily of oxybutynin.

Author(s): Birns J, Lukkari E, Malone-Lee JG

Affiliation(s): Department of Medicine, University College London Hospital, Leiras Oy Clinical Research, Helsinki, Finland.

Publication date & source: 2000-05, BJU Int., 85(7):793-8.

Publication type: Clinical Trial; Randomized Controlled Trial

OBJECTIVE: To compare the efficacy of a controlled-release (CR) formulation of oxybutynin with that of conventional oxybutynin in patients with detrusor instability or detrusor hyper-reflexia whose symptoms were stabilized on conventional oral oxybutynin tablets. PATIENTS AND METHODS: The study comprised a randomized, double-blind, parallel-group trial involving 130 patients drawn from 15 centres in the UK. The study was of 6 weeks' duration, i.e. 2 weeks of screening whilst taking conventional oxybutynin tablets (5 mg twice daily) followed by 4 weeks of double-blind treatment with either CR oxybutynin tablets (10 mg once daily) or conventional oxybutynin tablets (5 mg twice daily). Outcome measures were changes in 24-h frequency and 24-h incontinence episodes recorded throughout the study on diary charts. Adverse events were recorded by patients in their diary charts and serum concentrations of oxybutynin and its active metabolite, N-desethyloxybutynin, were measured at baseline and at completion of the study to detect possible drug accumulation. RESULTS: The treatments did not differ significantly in any of the outcome measures. The primary efficacy criterion was the daytime continence at completion of the study; 53% and 58% of patients were continent on CR and conventional oxybutynin treatments, respectively (the 95% confidence interval of the difference in the proportion being - 22% to 13%; P = 0.62). The total number of side-effects experienced by those patients receiving treatment with the CR formulation was 57% of that for patients receiving treatment with conventional oxybutynin. Individual side-effects showed a similar distribution within treatment groups. There was no evidence of the accumulation of oxybutynin or N-desethyloxybutynin during the multiple dosing of CR or conventional oxybutynin tablets. CONCLUSION: The CR and conventional formulations of oxybutynin did not differ in their efficacy, and the CR formulation was associated with fewer side-effects. In addition, CR oxybutynin appeared to maintain therapeutic blood levels over the 24 h dosing interval with no accumulation of oxybutynin or its active metabolite. Once-daily dosing with a CR tablet is seen as convenient for the patient and is expected to result in improved compliance in patients already stabilized on conventional oxybutynin treatment.