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.

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.