Differential vascular alpha(1)-adrenoceptor antagonism by tamsulosin and terazosin

Aims In patients with lower urinary tract symptoms suggestive of benign pro static obstruction the alpha(1)-adrenoceptor antagonist terazosin lowers bl ood pressure whereas only very small if any alterations were reported with the alpha(1)-adrenoceptor antagonist tamsulosin. Therefore, we have compare d the vascular alpha(1)-adrenoceptor antagonism of tamsulosin and terazosin directly. Methods Ten healthy subjects were investigated in a randomized, single-blin d, three-way cross-over design and received a single dose of 0.4 mg tamsulo sin, 5 mg terazosin or placebo on 3 study days at least 1 week apart. Befor e and 1, 3, 5, 7, 10 and 23.5 h after drug intake, alterations of diastolic blood pressure and other haemodynamic parameters in response to a graded i nfusion of the alpha(1)-adrenoceptor agonist phenylephrine were determined non-invasively. Results At most time points tamsulosin inhibited phenylephrine-induced dias tolic blood pressure elevations significantly less than terazosin (5 h time point: median difference in inhibition 35%, 95% CI: 18.7-50.3%). On the ot her hand, phenylephrine-induced changes of cardiac output, heart rate and s troke volume were similar during both active treatments. Conclusions In doses equi-effective for treatment of lower urinary tract sy mptoms tamsulosin causes less inhibition of vasoconstriction than tetrazosi n.