Pharmacokinetic studies with 3H-cytisine.

The pharmacokinetic behaviour of cytisine was studied in mice by means of tritiated cytisine after intravenous and oral administration of a sublethal dose of 2 mg/kg. After oral administration the maximum blood level is reached after 2 h. The absorption rate is approximately 42%. From the blood level after intravenous administration a half-life of 200 min was calculated. Within 24 h after intravenous administration 32% and after oral administration 18% of the administered radioactivity was excreted into urine. Following intravenous administration 3% of the dose was found in the faeces within 6 h. Among the examined organs and tissues the highest concentrations were reached in the liver, adrenals and kidneys. In the bile the highest concentration after intravenous administration was 200 times that in the blood.