[Usefulness of midazolam in a modified NLA--study on plasma concentrations]

Midazolam 0.2mg.kg-1 or diazepam 0.2mg.kg-1 was used as an induction agent in a modified NLA. Plasma concentrations of midazolam or diazepam were measured with benzodiazepines screen method, which was based on enzyme immunoassay. Pharmacokinetic analysis is based on the plasma concentration-time courses after a bolus injection. The distribution half-life (T alpha 1/2) of midazolam, 1.24 minutes, was shorter than that of diazepam, 3.85 minutes. The elimination half-life (T beta 1/2) of midazolam, 5.44 hours, was similar to that of diazepam, 5.02 hours. The initial fall-off in the alpha-phase was due to the distribution of the drug from plasma to the peripheral compartment, while the drop in the beta-phase was caused by redistribution from the peripheral compartment and total elimination of the drug. Midazolam was thought to be useful as an induction agent in a modified NLA, because midazolam is distributed to the peripheral compartment faster than diazepam. As midazolam has a long elimination half-life as that of diazepam, prolongation of its effects has to be considered when a large dose or continuous infusion is employed.