Plasma levels of (+) and (-)-propranolol and 4-hydroxypropranolol after administration of racemic (+/-)-propranolol in man.

1 We have given fifteen healthy volunteers single doses of racemic (+/-)-propranolol orally (40 mg) and intravenously (5-10 mg) to find out how large the variation was of the ratio between (-)- and (+)-propranolol plasma levels in relation to that of total levels of propranolol and 4-hydroxypropranolol. 2 Total propranolol (+/-)-levels 2 h after a 40 mg oral dose of (+/-)-propranolol varied from 21 to 580 nmol/l and those of 4-hydroxypropranolol from 0 to 33 nmol/l. Their levels did not correlate. The ratio between (-)- and (+)-propranolol levels varied from 0.99 to 2.04. The plasma half-lives of the two isomers were usually similar. 3 We conclude that in most single doses studies on relationships between plasma concentrations and effects (beta-adrenoceptor blockade) it is not necessary to quantitate (+)- and (-)-propranolol levels separately since total (+/-) plasma propranolol levels varied much more than the ratio between (-)- and (+)-propranolol.