Comparison of Silodosin and Naftopidil for Efficacy in the Treatment of Benign Prostatic Enlargement Complicated by Overactive Bladder: A Randomized, Prospective Study (SNIPER Study)

Purpose: We investigated the efficacy of 2 alpha 1-blockers with different affinities for the alpha 1-adrenoceptor subtypes silodosin and naftopidil in the treatment of benign prostatic enlargement complicated by overactive bladder. Materials and Methods: This was a prospective, open label, randomized, multicenter study of 350 outpatients with untreated benign prostatic enlargement associated with urinary urgency at least once per week and an OABSS (Overactive Bladder Symptom Score) of 3 or greater. Patients were randomly assigned to receive silodosin 8 mg per day or naftopidil 75 mg per day. Changes in parameters from baseline to 4 and 12 weeks were assessed based on I-PSS (International Prostate Symptom Score), I-PSS quality of life, OABSS and voiding functions measured by uroflowmetry. Results: On efficacy analysis a total of 314 patients were included in the 2 groups. No significant difference in adverse effects was observed between the groups. Mean I-PSS and I-PSS quality of life scores, and OABSS significantly improved in both groups. Statistically significantly greater improvement in the silodosin group than in the naftopidil group was observed in total OABSS (p = 0.03), I-PSS quality of life score (p = 0.005) and OABSS urgency score (p < 0.001) at 12 weeks. In regard to voiding function the maximum urinary flow rate showed significant improvements in both groups but the change in the maximum flow rate in the silodosin group at 12 weeks was significantly greater than in the naftopidil group (3.6 vs 2.1 ml per second). Conclusions: Silodosin, a pure alpha 1A-adrenoceptor blocker, showed greater improvement in overactive bladder symptoms along with the urinary flow rate in patients with benign prostatic enlargement complicated by overactive bladder compared to naftopidil, an alpha 1D>A-adrenoceptor blocker.