Pharmacokinetics of i.v. and rectal methohexitone in children.

The pharmacokinetics of methohexitone were investigated in 15 healthy children undergoing minor surgery under inhalation anaesthesia. Six received 1% methohexitone 1-2 mg kg-1 i.v. and nine received 10% methohexitone 20-25 mg kg-1 per rectum. On i.v. administration, three-compartment pharmacokinetics generally applied. The mean elimination half-life of methohexitone was 193 +/- 75 min; that is, considerably longer than previously reported for children, but in good agreement with findings in adults. The mean clearance was 17.9 +/- 8.3 ml min-1 kg-1, the volume of distribution at steady state was 2.1 +/- 0.24 litre kg-1 and the mean residence time was 134 +/- 47 min. The pharmacokinetic model used for the i.v. data was easily modified to suit the plasma concentration curves obtained on rectal administration. The mean bioavailability of methohexitone administered per rectum was 17%, with a six-fold variation between individuals.