Coadministration of tamsulosin and three antihypertensive agents in patients with benign prostatic hyperplasia: Pharmacodynamic effect

Tamsulosin, an alpha(1A)-adrenoceptor antagonist, has recently been approved to treat patients with symptomatic benign prostatic hyperplasia (BPH). Tamsulosin is highly selective for prostatic receptors with minimal affinity for vascular receptors. Therefore, it should have little effect on blood pressure and should not potentiate other agents' antihypertensive activity. To test this hypothesis,we conducted three randomized, double-masked, placebo-controlled studies to evaluate how coadministration of tamsulosin would affect the pharmacodynamic profiles of nifedipine, enalapril, and atenolol. Each study enrolled 12 hypertensive men aged 45 years or older whose blood pressure was being controlled with maintenance doses of nifedipine (study 1), enalapril (study 2), or atenolol (study 3). All 36 subjects were treated with placebo for 5 days and then randomly assigned to either placebo (control group) or tamsulosin therapy (0.4 mg/d for 7 days followed by 0.8 mg/d for 7 days) in addition to continuing their maintenance antihypertensive therapy. Blood pressure and pulse rate were monitored over a 24-hour period on study days 4, 11, and 19. Coadministration of tamsulosin in these small studies had no clinically significant effects on the pharmacodynamic action of nifedipine, enalapril, or atenolol; it produced no clinically significant differences in pulse rate and blood pressure, did not alter electrocardiographic or Holter monitoring results, and did not cause increased side effects. Coadministration of tamsulosin with the three antihypertensive agents studied had a favorable safety profile. Our results in these small studies indicate that the dose of nifedipine, enalapril, or atenolol did not require adjustment in patients given tamsulosin, which may give tamsulosin an advantage over other alpha-blocking agents used to treat patients with BPH. Now that tamsulosin has been approved in the United States, further clinical use may confirm these findings.