Objective: The aim of this study was to evaluate the effectiveness of oxybutynin in the treatment of nocturia in patients with overactive bladders (OAB) and to assess predictive factors for the responses to oxybutynin. Patients and Methods: Patients with symptoms of OAB and nocturia for more than 3 months were enrolled. A 2.5 mg dose of oxybutynin was given twice daily for 1 week after a baseline study that included a self-administered nocturia questionnaire, uroflowmetry, and frequency/volume chart. Outcome analysis included changes in nocturia episodes, uroflowmetry, and post-void residual urine. Patients were stratified according to a nocturia index (Ni), nocturnal polyuria index (NPi), and nocturnal bladder capacity index (NBCi). Results: A total of 59 patients were eligible for analysis. After 1 week of treatment with oxybutynin, the mean number of nocturia episodes had reduced from 2.7 ± 1.3 to 2.3 ± 1.1 (p <0.01). There were no statistically significant differences in the mean reduction of nocturia episodes between the subgroup of patients with NPi ≤ 0.35 and those with NPi > 0.35 (-0.4 vs. -0.3, p = 0.34, ANCOVA). Reduction in number of nocturia episodes was more significant in patients with Ni ≤ 1.5 than in those with Ni > 1.5 (-0.9 vs. -0.2, p = 0.03, ANCOVA), and in patients with NBCi > 2 than in those with NBCi ≤ 2 (-1.1 vs. -0.2, p = 0.01, ANCOVA). Conclusion: Ni and NBCi are good predicting factors for the effects of antimuscarinic agents on nocturia in patients with OAB.
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