Springer Online Journal Archives 1860-2000
Chemistry and Pharmacology
Summary A dose-ranging study was performed to compare the β1-adrenoceptor selectivity of bisoprolol with that of atenolol and nadolol. Seven normal subjects (mean age 26 y) were given single oral doses of bisoprolol 5 mg (B5), 10 mg (B10), 20 mg (B20); atenolol 50 mg (A50), 100 mg (A100); nadolol 40 mg (N40); and placebo (PL), in a single blind randomised cross-over design. β2-adrenoceptor responses were assessed by attenuation of finger tremor and cardiovascular responses to graded isoprenaline infusions. Dose-response curves were constructed, and doses of isoprenaline required to increase finger tremor by 100% (IT100), heart rate by 25 beats/min (IH25), SBP by 25 mm Hg (IS25), cardiac output by 35% (IC35), and decrease DBP by 10 mm Hg (ID10), after each treatment were calculated. These indices were compared with placebo response and expressed as dose-ratios. Exercise heart rate (EHR) was used to assess β1-adrenoceptor blockade. There were dose-related increases in plasma concentrations of bisoprolol and atenolol. Reduction of EHR was significantly less with B5 (16.8%) in comparison with all other treatments: B10 21.9%, B20 23.1%; A50 22.5%, A100 22.6%; N40 22.9%. There were small but significant reductions in isoprenaline-induced tachycardia with bisoprolol and atenolol, although mean dose-ratios were considerably less in comparison with N40 (IH25 dose-ratios): B5 2.55, B10 3.18, B20 3.93, A50 2.91, A100 4.89, N40 17.23. There were similar patterns for the other isoprenaline responses. These results show that conventional doses of bisoprolol (10 mg) and atenolol (50 mg) produced equal antagonism of β1 and β2-adrenoceptors, and therefore possess equal degrees of β1-adrenoceptor selectivity. Increasing doses of bisoprolol and atenolol were associated with partial loss of selective β1-adrenoceptor blockade, although antagonism of β2-adrenoceptors was significantly less compared with the effects of nadolol.
Type of Medium: