Plasma levels and excretion of two beta-adrenoceptor blocking drugs 3H-exaprolol and 3H-propranolol were observed up to 96 h after a single i.v. administration to rats. Terminal half-lives of 26.8 +/- 9.1 h and 51.3 +/- 7.5 h were found for exaprolol and propranolol, respectively. The recovery of 3H radioactivity in feces following i.v. administration of the drugs (34.2 +/- 0.8 per cent and 12.0 +/- 1.3 per cent 3H of exaprolol and propranolol, respectively) is of biliary origin, as 30.7 +/- 3.5 per cent and 13.4 +/- 3.6 per cent 3H of exaprolol and propranolol, respectively, was excreted in the bile after i.v. administration. Enterohepatic circulation of the drugs was studied using the donor-recipient rat method. After intraduodenal administration of donor bile to the recipient rat approximately 50 per cent and 40 per cent of the biliary 3H activity of exaprolol and propranolol, respectively, was re-excreted following absorption. A formula for calculating the amount of the substance together with its metabolites excreted in the bile, urine or feces as a result of enterohepatic circulation has been proposed.

The disposition of the beta adrenoceptor blocking drug 1-(2-cyclohexylphenoxy)-3-isopropylamino-2-propanol, exaprolol, in organs of the rat has been studied. After i.v. administration of 3H-exaprolol a transient extremely high accumulation of the drug in lungs was observed with a peak of 7.7% of dose/g 30 min post-administration. The disposition pattern in heart, kidneys and liver may be characterized by a tissue to plasma ratio about ten. Lower exaprolol tissue levels were observed after oral administration. The tissue to plasma ratios showed an initial increase followed by constant levels. The distribution of exaprolol in organs of the rat is discussed in the light of the previously determined pharmacokinetic parameters.