Methohexital plasma concentrations in children following rectal administration.

Despite the increasing use of rectal methohexital as a premedicant-induction agent in pediatric anesthesia, there are no data to confirm the assumption that low plasma methohexital concentrations are the cause of inadequate sedation of children and that high concentrations are associated with the loss of consciousness. Plasma methohexital concentrations were determined in 20 ASA Class I children, ages 2-7 yr, after the rectal administration of methohexital (25 mg/kg). Seventeen of the 20 children in this study fell asleep after receiving the drug and achieved peak plasma concentrations greater than 2 micrograms/ml. The maximum plasma methohexital concentration in children that did not fall asleep was less than 2 micrograms/ml. The mean time to the onset of sleep after drug administration was 8.3 min (at which time the mean plasma concentration was 4.4 micrograms/ml). The mean peak plasma concentration and the mean time to peak plasma concentration were 4.7 micrograms/ml and 13.9 min, respectively. Loss of consciousness after rectal administration of methohexital correlates well with the plasma concentration of the drug.