Objectives: To compare the effect of treatment with silodosin 4mg once daily versus that of silodosin 4mg twice daily on storage symptoms in Japanese patients with benign prostatic hyperplasia. Methods: A prospective, multicenter, 12-week, open-labeled study randomized a total of 268 men aged 50years or older with benign prostatic hyperplasia and overactive bladder to silodosin 4mg/day or 8mg/day. Changes in the end-points of the average value of International Prostate Symptom Score, quality of life index in the International Prostate Symptom Score, Overactive Bladder Symptom Score and urodynamic parameters were evaluated. The change in the storage symptom subtotal score of the International Prostate Symptom Score was considered as the primary end-point. Results: Silodosin 4mg/day was not inferior to silodosin 8mg/day in regard to the primary end-point. In contrast, the efficacy of treatment with silodosin 4mg twice daily was greater than that of 4mg once daily, based on both the quality of life index and the Overactive Bladder Symptom Score total score. There was a discrepancy between the scores evaluated using the International Prostate Symptom Score and Overactive Bladder Symptom Score questionnaires. Conclusions: Silodosin 4mg once daily is not inferior to silodosin 4mg twice daily in regard to storage symptoms score evaluated by the International Prostate Symptom Score. In contrast, silodosin 4mg twice daily is more effective on storage symptoms evaluated by the Overactive Bladder Symptom Score than silodosin 4mg once daily.
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