[Pharmacological properties of naftopidil, a drug for treatment of the bladder outlet obstruction for patients with benign prostatic hyperplasia].

Naftopidil, a phenylpiperazine derivative, is a novel alpha 1-adrenoceptor antagonist and is new drug for the bladder outlet obstruction in patients with benign prostatic hyperplasia (BPH). Naftopidil competitively inhibited specific [3H]prazosin binding in prostatic membranes of humans, and its Ki value was 11.6 nM. Using cloned human alpha 1-adrenoceptor subtypes (alpha 1a, alpha 1b and alpha 1d), naftopidil was selective for the alpha 1d-adrenoceptor with approximately 3- and 17-fold higher affinity than for the alpha 1a- and alpha 1b-adrenoceptor subtypes, respectively. In anesthetized dogs, naftopidil selectively inhibited the phenylephrine-induced increase in prostatic pressure compared with mean blood pressure. The selectivity of naftopidil for prostatic pressure was more potent than those of tamsulosin and prazosin. In conscious rabbits, the effect of naftopidil on the blood pressure reactions following the tilting was less potent than those of tamsulosin and prazosin. In clinical studies, naftopidil has been demonstrated to be effective in the treatment of bladder outlet obstruction in patients with BPH. In Japan, naftopidil has been already approved for clinical use as a drug for BPH.