Age-dependent pulmonary first-pass elimination of propranolol in rats

Plasma levels of propranolol after 2.5 mg kg−1 given i.v. and i.a. have been compared in 3- to 4-week-old rats to evaluate the effect of age on pulmonary first-pass elimination of the drug. In 5- to 52-week-old rats, the area under the plasma concentration-time curve (AUC) after an intra-arterial dose was always larger than that after the i.v. dose. The plasma elimination half-lives after both routes of administration were almost identical, but tended to increase with age between weeks 7 and 104. First-pass pulmonary clearance and extraction ratio tended to decrease with age between weeks 7 and 52.