Differential vascular α1‐adrenoceptor antagonism by tamsulosin and terazosin

Abstract

Aims In patients with lower urinary tract symptoms suggestive of benign prostatic obstruction the α₁‐adrenoceptor antagonist terazosin lowers blood pressure whereas only very small if any alterations were reported with the α₁‐adrenoceptor antagonist tamsulosin. Therefore, we have compared the vascular α₁‐adrenoceptor antagonism of tamsulosin and terazosin directly. Methods Ten healthy subjects were investigated in a randomized, single‐blind, three‐way cross‐over design and received a single dose of 0.4 mg tamsulosin, 5 mg terazosin or placebo on 3 study days at least 1 week apart. Before 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 infusion of the α₁‐adrenoceptor agonist phenylephrine were determined non‐invasively. Results At most time points tamsulosin inhibited phenylephrine‐induced diastolic blood pressure elevations significantly less than terazosin (5 h time point: median difference in inhibition 35%, 95% CI: 18.7–50.3%). On the other hand, phenylephrine‐induced changes of cardiac output, heart rate and stroke volume were similar during both active treatments. Conclusions In doses equi‐effective for treatment of lower urinary tract symptoms tamsulosin causes less inhibition of vasoconstriction than terazosin.