Plasma concentrations of diazepam and its metabolites after peroral, intramuscular, and rectal administration. Correlation between plasma concentration and sedatory effect of diazepam.

Plasma levels of diazepam, N-demethyldiazepam and free oxazepam were measured gaschromatographically in ten healthy volunteers after 5 mg of diazepam perorally, intramuscularly and rectally (with three different kinds of suppositories). The best absorption of diazepam was found after peroral administration. After an intramuscular injection a delayed absorption with low plasma concentrations of diazepam was found. The basal component of a diazepam suppository seems to have a great effect on the rectal absorption of diazepam. Two of the three different kinds of diazepam suppositories caused higher plasma diazepam concentrations than the intramuscular injection of the drug. There were no great differences in the amount of the metabolites of diazepam after different kinds of administration. The subjective sedatory effect of diazepam lasted approximately as long as the fast distribution of diazepam from plasma took place. A very highly significant correlation between plasma concentration and subjective sedatory effect of diazepam after a single dose was found.