[Pharmacokinetic studies following intravenous, intramuscular and rectal administration of methohexital in children]

Abstract

In pediatric patients methohexitone is used increasingly in different application forms for induction of anesthesia. Plasma concentrations of methohexitone were measured after rectal induction with 25 mg/kg, and after intramuscular injection of 5 mg/kg in 10 children each aged 2-7 years and were compared with 4 children after intravenous administration of 2 mg/kg. The pharmacokinetic parameters of the i.v. administered methohexitone were calculated and compared with the known pharmacokinetics in adults, showing that the open two-compartment-model is also applicable to children with a substantial shorter beta-half-life and a higher clearance. After rectal and i.m. induction with methohexitone the individual plasma concentrations scatter in a relatively wide range. The mean value curves of both application forms are similar with a maximum plasma concentration of 2.76 micrograms/ml between minutes 7-15 (rectal) respectively 2.6 micrograms/ml between minutes 15-30 (i.m.); 2 h later they are 0.57 micrograms/ml (rectal) and 1.03 micrograms/ml (i.m.). In contrast to the 100% available bioactivity of methohexitone after i.m. administration it amounts to only about 17% after rectal induction. As a result one can consider children to be able to eliminate methohexitone sufficiently in the observed plasma concentration range.