Triazolam pharmacokinetics in rats using a radioreceptor assay

The time course of the activities arising after oral (0.33 and 1 mg/kg) and intravenous (0.33 mg/kg) administration of triazolam to rats was assessed in different tissues using a radioreceptor assay. In almost all cases the activities in plasma were lower than in liver, brain, kidney and heart showing that the drug and possibly some active metabolites distribute extensively and rapidly in all the sampled tissues. Peak plasma levels were 34 pmol/ml, 10.2 pmol/ml and 34.9 pmol/ml after 0.33 mg/kg intravenously, 0.33 mg/kg per os and 1 mg/kg p.o. respectively. The area under curve in plasma was proportional to the administered oral dose and it was much smaller after intravenous injection than after the equivalent oral dose (13.8 pmol.h/ml after the i.v. dose and 47.3 pmol.h/ml after the oral dose).