Rapaflo (silodosin): Alpha-blocker approved for the treatment of benign prostatic hyperplasia (BPH)

Silodosin is a selective alpha-1 adrenergic receptor antagonist. By blocking these receptors, silodosin causes the smooth muscle in the human prostate, bladder base, bladder neck, prostatic capsule, and prostatic urethra to relax, which results in an improved urine flow and a reduction in the symptoms of benign prostatic hyperplasia (BPH). This agent was approved on October 8, 2008, for the treatment of the signs and symptoms of BPH.

Efficacy. The efficacy of silodosin was assessed in two 12-week, randomized, double-blind, placebo-controlled, multicenter studies. Patients (N=923) were randomized to treatment with either silodosin 8 mg/d or placebo. The primary efficacy outcome was the International Prostate Symptom Score (IPSS), which measured irritative and obstructive symptoms. Patients treated with silodosin demonstrated significant improvements in IPSS from baseline to Week 12 in both Study 1 (mean change with silodosin, –6.5; mean change with placebo, –3.6; P<.0001) and Study 2 (mean change with silodosin, –6.3; mean change with placebo, –3.4; P<.0001).

Safety. Patients treated with silodosin may experience postural hypotension or syncope. Because BPH and prostate cancer cause many of the same symptoms and frequently coexist, patients should be assessed for carcinoma of the prostate before they begin treatment with silodosin. Intraoperative floppy iris syndrome has occurred during cataract surgery in some patients treated with alpha-1 blockers. The most common adverse events associated with silodosin treatment include retrograde ejaculation, dizziness, diarrhea, orthostatic hypotension, headache, nasopharyngitis, and nasal congestion.