Determining zolpidem compliance: Urinary metabolite detection and prevalence in chronic pain patients

David M. Schwope, Anne DePriest, David L. Black, Yale H. Caplan, Edward J. Cone, Rebecca Heltsley

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


Zolpidem (Ambien®) is the most prescribed insomnia treatment in the USA; however, little is known about zolpidem metabolite excretion in chronic pain patients. As zolpidem is extensively metabolized in vivo to zolpidem 4-phenyl carboxylic acid (ZCA), metabolite detection may provide improved accuracy for compliance determinations, thereby improving clinical decisions. Zolpidem and ZCA were extracted from 1 mL human urine by mixed-mode solid-phase extraction. Samples were analyzed by LC-MS-MS using positive electrospray ionization with multiple reaction monitoring mode employed for detection and quantification. Gradient chromatographic separation was achieved with a reversed-phase column in a rapid 1.8 min analysis. The assay was linear from 4 to 1,000 μg/L for zolpidem and 4 to 10,000 μg/L for ZCA. Interday recovery (bias) and imprecision (n 5 20) were 100-107% of target and 2.4-3.7% relative standard deviation, respectively. Extraction efficiencies were 78-90%. Pain compliance samples (n 5 3,142) were de-identified and analyzed for zolpidem and ZCA. Zolpidem was detected greater than limit of quantification in 720 specimens (22.9%), while ZCAwas detected in 1,579 specimens (50.3%). Only five specimens contained zolpidem alone. ZCA was observed without parent zolpidem in 864 specimens, thereby increasing population detection rates by 27.5%. Addition of a zolpidem metabolite to compliance determinations substantially improved detection for zolpidem intake and also should prove useful in clinical and forensic settings.

Original languageEnglish (US)
Pages (from-to)513-518
Number of pages6
JournalJournal of analytical toxicology
Issue number8
StatePublished - Oct 1 2014

ASJC Scopus subject areas

  • General Medicine


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