A simple and rapid method for the identification of zolpidem carboxylic acid in urine

Zolpidem is a non-benzodiazepine hypnotic that has been implicated in both drug-facilitated sexual assault and drink spiking. Detection of the drug in urine is extremely difficult because of its extensive metabolism. A method is presented for the detection and quantitation of zolpidem carboxylic acid (ZCA), the major urinary metabolite of zolpidem. The metabolite was extracted from urine at pH 4.5-5.0 with chloroform/isopropanol alkylated with ethyl iodide and identified by gas chromatography-mass spectrometry in the selected ion-monitoring mode. Following a single ingestion of 10 mg zopidem, ZCA is detected for up to 72 h. The limit of detection is 2 ng/mL, with an overall recovery of 80%. Using this procedure, zolpidem was identified in two cases of alleged drug-facilitated sexual assault.