1 Plasma levels of propranolol were measured at intervals after the oral administration of 160 mg propranolol and 160 mg L.A. propranolol in ten subjects who received both drugs on separate occasions.2 Mean peak plasma concentration of propranolol occurred 2 h after propranolol and 10 h after the L.A. formulation; the peak concentration with the former was four times that with the latter. At 24 h the plasma level was significantly higher after L.A. propranolol. 3 Observations were made in nine healthy volunteers who exercised before and at intervals after the oral administration of 160 mg propranolol and 160 mg L.A. propranolol.4 Propranolol produced a maximum reduction (27.84 + 2.4%) in the exercise tachycardia at 3 h and L.A. propranolol a maximum reduction (22.00 + 1.73%) at 6 h. The effects at 24 h were 9.24 + 1.55 and 16.79 + 2.16% respectively.5 Five subjects were given 160 mg propranolol as a single dose daily for 8 days and on a separate occasion similar treatment with L.A. propranolol. Subjects were exercised and blood samples were taken before and 3 h after each dose on days 1 to 5 and on day 8. propranolol were 12.5 to 17.5 (trough values) and 18.4 to 50.0 (peak values) ng/ml. 8 These observations show that the new long acting formulation of propranolol produces a significant reduction of an exercise tachycardia throughout a 24 h period without a very high initial effect during single and multiple dosing. This formulation should be suitable for once a day administration.

Observations were made in 5 healthy subjects who exercised before and 1, 3, 6, 8 and 24 h after the oral administration on separate occasions of 160 mg oxprenolol, 160 mg slow release oxprenolol, 160 mg long acting propranolol and 400 mg sotalol. Blood samples were obtained before and at 1, 2, 3, 6, 8, 10 and 24 h after drug administration and assayed for drug concentration. Although the plasma concentration of oxprenolol after S.R. oxprenolol was significantly less at 1 and 2 h and significantly greater at 24 h than after conventional oxprenolol, there was little difference between the effects of the two drugs on an exercise tachycardia. The plasma level of propranolol and the reduction in an exercise tachycardia after L.A. propranolol increased slowly to reach a peak at 6 h and then declined gradually to 24 h. The maximum plasma concentration and effect after sotalol occurred at 3 h and then declined with an elimination half-life of 12.1 h. At 24 h the percentage reduction in an exercise tachycardia was 8.3 +/- 2.5 after oxprenolol, 10.0 +/- 2.3 after S.R. oxprenolol, 18.0 +/- 3.2 after L.A. propranolol and 14.7 +/- 3.4% after sotalol.

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 f-adrenoceptor antagonist with a long duration of effect on an exercise tachycardia and a long plasma elimination half-life.

The mean increase over baseline for the young subjects was 2.0 pmol/106 cells at a concentration of 10-8 M isoprenaline and rose to a maximum (11.3 pmol/106 cells) at 10-1 M isoprenaline. In the elderly subjects the mean concentration of cAMP at 10-1 M isoprenaline showed no increase over baseline while a maximum (5.4 pmol/106 cells) was observed at 10-4 M isoprenaline. The increase in cAMP in both young and old was a linear function of the log concentration of isoprenaline between 10-I M and 10-6 M isoprenaline. Covariance analysis of these linear portions showed no significant difference in slopes, but there was a significant difference in elevation (P < 0.01) with the line for the elderly displaced to the right.These findings support the suggestion that altered receptor function plays a role in the changed responsiveness to drugs observed in the elderly. In particular, they are consistent with the observation of Shand, Vestal & Woods (1978) of a decreased cardiac responsiveness to isoprenaline in the elderly.

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1. The effects of 160 mg of propranolol and 160 mg of a long-acting (LA) formulation of propranolol were studied in healthy subjects. 2. Both drugs reduced an exercise tachycardia but the peak was less and the 24 h effect greater after long-acting propranolol than after propranolol. 3. These differences were maintained on repeated dosing for 8 days. 4. In contrast to single doses of 400 mg of sotalol, 160 mg of oxprenolol and 160 mg of slow-release oxprenolol, the peak effect of long-acting propranolol was less and that at 24 h was greater.

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