Purpose: This study was designed to test the power potential of a number of different clinical trial designs that could be deployed to test the efficacy of an antimuscarinic drug against bladder retraining.
Materials and methods: This was an observational cohort study. Data were collected prospectively from patients treated for an overactive bladder by antimuscarinic agents with bladder retraining, or by bladder retraining alone. At initiation and at followup data on frequency, incontinence, urgency and urge incontinence were collected. Data from visits up to 16 weeks of treatment were analyzed using the parametric methods.708 patients were studied, 44 males and 664 females, and their mean age was 54 (sd 22). 52 patients used pure bladder retraining and 656 used bladder retraining and an antimuscarinic agent. The drug was oxybutynin, tolterodine or imipramine combined with oxybutynin or tolterodine as combination therapy.
Results: A between groups analysis demonstrated that bladder retraining was associated with a greater improvement in urinary frequency compared to antimuscarinic therapy (Z = -4.6, 95% CI of difference -3.3, -1.4, p <0.001) whereas antimuscarinic therapy was associated with a greater improvement in incontinence compared to bladder retraining (Z = -2.6, 95% CI of difference -0.93, -0.27, p = 0.024). The within group change in incontinence episodes in the bladder retraining group did not appear to show an effect (95% CI of change -0.19, 0.43). A subgroup showing greatest DeltaInc was sought. Boxplots of DeltaInc against age group, sex and the grading of symptoms were examined for maximum effect. Female sex, age group of 50 or greater and patients describing urge incontinence demonstrated the greatest DeltaInc. Their mean daily frequency was 11.45 (sd 6.1) and incontinence 1.6 (sd 2.1). A sample with such characteristics would be most sensitive to treatment effect. The bladder retraining group had a higher daily frequency (Z = -3.2, p = 0.001, 95% CI for bladder retraining 10 to 11, 95% CI for antimuscarinic group 10 to 12) and a lower daily incontinence compared to the antimuscarinic group (Z = -3.4, p <0.001, 95% CI of median for bladder retraining 0.75, 0.85, 95% CI of median for antimuscarinic group 0.75, 1.75).
Conclusions: Change in frequency is a poor outcome measure, DeltaInc is significantly superior. An antimuscarinic tested against bladder retraining, using DeltaInc for outcome, would probably compare favorably.