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Effect of Prostate Volume on Silodosin-Mediated Improvement of Symptoms Associated With Benign Prostatic Hyperplasia
Steven A. Kaplan, MD1, Claus Roehrborn, MD2, Lawrence Hill, PharmD3, Weining Volinn, MS3, Gary E. Hoel, PhD3.
1Weill Cornell Medical College, New York, NY, USA, 2UT Southwestern Medical Center, Dallas, TX, USA, 3Watson Laboratories, Inc., Salt Lake City, UT, USA.

Background: Results combined from 2 placebo-controlled phase 3 studies in patients with symptoms of benign prostatic hyperplasia (BPH) demonstrated significant improvement in International Prostate Symptom Score (IPSS) and peak urinary flow rate (Qmax) with silodosin. This retrospective analysis examined the effect of estimated prostate volume (PV) on symptom improvement in patients who received silodosin.
Methods: PV was estimated based on prostate-specific antigen (PSA) levels and age using a published algorithm (Roehrborn CG, et al. Urology.1999;53:581-589). Patients who received silodosin were stratified by estimated PV into 2 groups according to whether they had estimated PV <30 mL or estimated PV ≥30 mL. Changes from baseline to week 12 (last observation carried forward) in total IPSS and Qmax were compared between the 2 groups by analysis of covariance.
Results: Of 466 patients given silodosin, 450 provided PSA baseline data. Estimated PV values ranged from 18.4 to 76.8 mL, and 100 patients had estimated PV <30 mL. IPSS and Qmax baseline values for the 2 groups were very similar (Table). Decreases in IPSS from baseline to week 12 were numerically greater in patients with estimated PV ≥30 mL, but the adjusted mean difference in IPSS changes from baseline between the 2 subgroups was not statistically significant (Table). Mean increase in Qmax from baseline to week 12 was ≥2.3 mL/sec in both subgroups, consistent with clinically important urinary flow improvement in both subgroups.
Conclusions: Silodosin demonstrated clinically meaningful improvement in IPSS and Qmax, regardless of estimated sizes of prostate volume. Research funded by Watson Laboratories, Inc.

Table. Change from Baseline (CFB) in IPSS and Qmax by Estimated PV
PV <30 mL (N=100)PV ≥30 mL (N=350)
IPSSBaseline, mean ± SD21.0 ± 5.221.4 ± 5.1
CFB to week 12, mean ± SD-5.4 ± 6.4-6.7 ± 6.7
Adj. mean difference (95% CI)-1.2 (-2.6, 0.2)
Qmax,Baseline, mean ± SD8.9 ± 2.48.7 ± 2.6
mL/secCFB to week 12, mean ± SD3.3 ± 5.42.3 ± 4.1
Adj. mean difference (95% CI)-1.1 (-2.0, -0.1)
IPSS, International Prostate Symptom Score; PV, prostate volume; SD, standard deviation.

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