The effect of prazosin in benign prostatic hypertrophy, a placebo controlled double-blind study

It is well known that the smooth muscles of the bladder neck, the urethra and the prostatic capsule in man are rich in sympathetic ends, mainly alpha-adrenergics. The stimulation of these adrenoreceptors should cause an increase of urethral resistance and out-flow obstruction. This is the basis of the treatment of benign prostatic hypertrophy (BPH) with alpha-blocking agents such as phenoxybenzamine. It is suggested that prazosin, an alpha-1-adrenergic blocking agent, may prove preferable to phenoxybenzamine for clinical use because of its selective blocking action on the alpha-1-receptors. In this study eighteen BPH patients were submitted to a double-blind treatment with placebo or Prazosin. Clinical symptoms improved during Prazosin therapy with respect to controls (5% level of Wilcoxon's test). Urodynamic evaluation was performed before and after treatment and a statistically significant improvement of maximum urinary flow rate, average urinary flow rate and residual rate (residual volume/vesical volume x 100) was found in Prazosin patients (P < 0.001), (P < 0.05), (P < 0.05). The expected fall in intraurethral pressure was not observed. In three patients treated with Prazosin detrusor hyperreflexia disappeared. For these reasons, Prazosin, in spite of the poor effect shown on the urethra and bladder neck, seems to have a good therapeutic effect in BPH, particularly in patients with detrusor hyperreflexia (about 40% of BPH patients).