A propranolol radioimmunoassay and its use in the study of its pharmaco‐kinetics following low doses

A radioimmunoassay has been developed for propranolol with a sensitivity of 2.37 nmol l-1 in unextracted plasma using a 50 microliter sample. Plasma concentration measurements were made on samples from volunteers for up to 8 h after they had been given 5, 10, or 40 mg of propranolol by mouth. Analysis of the results showed that mean elimination half-lives and total body clearances were similar following each of the doses and that the area under the curve was proportional to the dose. Steady-state propranolol concentrations in 17 patients on regular propranolol treatment were linearly related to the dose ver the range 20-640 mg d-1; the regression line extrapolated to the origin. These data indicate non-saturable kinetics for the hepatic metabolism of propranolol within the dose ranges investigated and lead us to believe that there is no 'oral-threshold' dose for propranolol. The radioimmunoassay may be useful in clinical practice for monitoring plasma propranolol concentrations and for detecting patient compliance.