Comparison of the efficacy and pharmacokinetics of conventional propranolol and a long acting preparation of propranolol.

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. 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. 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. 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. 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. The reduction in the exercise tachycardia 3 h after propranolol ranged from 33.0 to 36.9% and 24 h after propranolol from 12.2 to 20.8%. The corresponding values after L.A. propranolol were 26.8 and 31.4 (3 h values) and 20.4 and 25.0 (trough values). The trough plasma levels of propranolol during administration of propranolol ranged from 10.2 to 19.4 ng/ml and peak values from 202.2 to 245.0 ng/ml. The corresponding values after L.A. propranolol were 12.5 to 17.5 (trough values) and 18.4 to 50.0 (peak values) ng/ml. 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.