Development of a Radioimmunoassay for the Determination of Zolpidem in Biological Samples

Abstract

The development of a specific and sensitive radioimmunoassay for the detection of zolpidem and its metabolites in urine and serum samples is described. The assay can be used to pre-screen forensic and emergency samples. 6-Methyl-2-(4-methylphenyl)imidazo[1,2-a]- pyridine-3-acetic acid was prepared as a hapten and was coupled directly and indirectly to bovine serum albumin. The immunization of rabbits with the hapten–bovine serum albumin conjugates resulted in the production of highly specific antibodies, showing no significant cross-reactivities towards existing drugs. The four- parameter logistic model was used to process the calibration data into a fitting curve (r² = 0.9764). Intra- and inter-assay relative standard deviations were <6.30 and <12.28%, respectively. The limit of quantification was 0.1 ng ml^–1. Using this assay, zolpidem levels were determined in urine and serum, and could be easily detected up to 48 h after oral intake of 10 mg of zolpidem.