Effects of prazosin and carbachol in patients with benign prostatic obstruction

To eight patients with benign prostatic obstruction (BPO), prazosin and placebo were given in a double blind cross-over manner. Prazosin decreased significantly residual urine volume and increased maximum and average flow rates. Neither when treated with prazosin nor with placebo, did the patients improve their ability to empty the bladder after injection of carbachol (0.25 mg) s.c. The only significant effect of carbachol on urodynamic variables was an increase in intravesical premicturition pressure. This was observed both when the patients were treated with prazosin and with placebo. Fourteen patients with BPO were given oral carbachol in maximally tolerated doses (6 or 12 mg/day) during a 2 week period. Despite producing significant systemic side effects in all patients, carbachol did not change any of the urodynamic variables tested. It is concluded that carbachol does not further improve bladder emptying in BPO patients given prazosin. Oral carbachol has no effects on bladder emptying in these patients.