Diazepam: Determination in Micro Samples of Blood, Plasma, and Saliva by Radioimmunoassay

Abstract

A radioimmunoassay (RIA) procedure has been developed with the necessary sensitivity for the determination of diazepam directly in micro samples of blood/plasma (10 µl) and saliva (100 µl) for up to 16 hours following oral administration of a single 5-mg dose of the drug to man. The method has been applied for the assay of 10-µl blood samples obtained by finger-stick that had been spotted on absorbent paper and as much as one week later eluted with buffer prior to analysis. This procedure provides a convenient approach for the collection, handling, and transportation of samples. When 100 human toxicology samples were screened blindly for the presence of diazepam, no false positive results were found as determined by a specific electron capture-gas chromatography (EC-GC) procedure. A good correlation (r = 0.99) was obtained when plasma samples from subjects chronically receiving diazepam were assayed for diazepam by the RIA and the EC-GC method. The ability to determine diazepam in saliva may provide the opportunity to evaluate its in vivo plasma protein binding and the possible influence of concomitant medication on this parameter.