K. Harada et al., A comparison of the antagonistic activities of tamsulosin and terazosin against human vascular alpha(1)-adrenoceptors, JPN J PHARM, 80(3), 1999, pp. 209-215
Tamsulosin, a selective alpha(1A)-adrenoceptor antagonist, and terazosin, a
non-selective one, are effective for the treatment of urinary disturbance
due to benign prostatic hypertrophy. In the present study, their al-adrenoc
eptor-blocking effects on blood vessels, which may cause orthostatic hypote
nsion, were investigated in 10 healthy males. After the subjects took orall
y 0.2 mg of tamsulosin, 1 mg of terazosin or a lactate capsule as the contr
ol in a randomized cross-over fashion, their finger tip vasoconstrictor res
ponse to cold stimulation and vasoconstrictor response of the dorsal hand v
ein to increasing doses of phenylephrine were examined. The finger tip vaso
constrictor response was significantly reduced and the infusion rate of phe
nylephrine producing a half-maximal constriction was significantly increase
d by terazosin, but tamsulosin had no significant effect on these parameter
s. These data suggest that the usual dose of tamsulosin exerts little alpha
(1)-adrenoceptor-blocking activity on blood vessels, and orthostatic episod
es might be mild, if any, during the treatment with tamsulosin.