Abstract
1 Observations were made in five subjects who exercised before and at 2, 3, 6, 8, 24, 33 and 48 h after the oral administration of placebo and 5, 10, 20 and 40 mg betaxolol. 2 The exercise heart rate remained constant at all times after the placebo. All doses of betaxolol significantly reduced the exercise tachycardia at all times. The maximum effect (34.4 +/- 2.2%) occurred after 40 mg. 3 There was a small decline in effect from the peak to 24 h when 40 mg produced a 23.3 +/- 2.7% reduction and a further decline to 48 h when there was a 14.6 +/- 1.8% reduction. 4 Plasma levels of betaxolol were measured in these studies. The peak plasma concentration occurred between 3 and 8 h with different doses. The plasma elimination half-lives after 10, 20 and 40 mg were 11.4 +/- 2.5, 15.9 +/- 4.9 and 15.1 +/- 3.1 h. 5 The effects of 40 mg betaxolol, 200 mg atenolol, 160 mg propranolol, 160 mg oxprenolol, 400 mg sotalol and placebo on an exercise tachycardia were compared in five subjects who received all treatments in random order. 6 There was no significant difference in the maximum reduction produced in an exercise tachycardia by the different drugs. 7 The effect of all drugs decreased with time. The effect of oxprenolol had worn off at 24 h but at 48 h only atenolol and betaxolol produced significant reductions in the exercise tachycardia. 8 Plasma concentrations of the different drugs were measured and plasma elimination half-lives determined. The half-life for betaxolol was 24.5 h which was longer than that for any of the other drugs. 9 These observations show that betaxolol is a potent beta-adrenoceptor antagonist with a long duration of effect on an exercise tachycardia and a long plasma elimination half-life.
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