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.