Effects of administration route on pharmacokinetics of aspirin in the rabbit.

The absorption of aspirin used in the form of lysine acetylsalicylate was studied in the rabbit. Each animal received the drug by three routes: intravenous, gastric and duodenal. Plasma concentrations of acetylsalicylic acid (ASA) and salicylic acid (SA) were compared. ASA plasma concentrations obtained after gastric or duodenal administration were low compared to those after intravenous injection. Concentrations were 2 to 5 times higher after gastric than duodenal administration. SA plasma concentrations were lower at the beginning of the experiment for gastric than for duodenal administration; after 90 min the concentrations were similar. A better absorption of aspirin (as lysine acetylsalicylate) after administration occurred in the stomach than in the duodenum, but the amount of ASA which reached the central compartment was quite poor.

Pharmacokinetics of intravenous and intramuscular methohexitone in dogs.

Twenty-four dogs received methohexitone, either intravenously injected (2 mg kg-1 of a 1% solution) or intramuscularly (10 mg kg-1 of a 2% solution). Plasma methohexitone concentrations were measured by gas/liquid chromatography and pharmacokinetics were obtained from the general equations of a multicompartment model. Peak blood concentrations were equivalent following i.v. (18.2 +/- 9.9 mg 1(-1); at 30 s) and i.m. (19.1 +/- 5.6 mg 1(-1); at 3 min) injections. After i.v. injection a rapid distribution phase (half-life t 1/2 lambda 1; 1.3 +/- 0.5 min) was followed by an elimination phase (elimination half-life t 1/2 lambda z; 26.4 +/- 7.8 min). After i.m. injection the distribution phase was followed by two further phases (half-lives: 10.1 +/- 3.6 min and 75.6 +/- 22.6 min). The authors conclude that an i.m. dose five times as great as the i.v. dose produces equivalent peak blood concentration 30 s after i.v. injection and 3 min after i.m. injection. In addition, after i.m. injection of 10 mg kg-1 an additional compartment was apparent, indication substantial drug uptake by poorly perfused tissues.