Zolpidem urine excretion profiles and cross-reactivity with ELISA(®) kits in subjects using Zolpidem or Ambien(®) CR as a prescription sleep aid.

Zolpidem, a Schedule IV controlled substance under the Federal Controlled Substance Act, has a rapid onset of action and short elimination half-life, rendering it ideal as a sleep aid. The crossreactivity of two zolpidem ELISA kits was investigated using patients taking a known administration of zolpidem. Subjects provided urine samples before, 30 min after their prescribed dose, and upon waking. Specimens were screened for zolpidem by ELISA (Immunalysis and Neogen) and then confirmed and quantitated for zolpidem using gas chromatography-mass spectrometry (GC-MS) confirmation in select ion monitoring mode. All samples were measured for creatinine and corrected accordingly. The ELISA screening results demonstrated that all samples, except one, screened positive by ELISA using both kits, even when the GC-MS data found no zolpidem in the patient's urine sample. The maximum concentrations of zolpidem ranged from 15 to 120 ng/mg creatinine. Two of the patients showed zolpidem concentrations of 10 ng/mg creatinine or above after 20 h post dose. The high variability and concentration range seen in these patients, all on similar doses, suggest wide variability in the metabolism of zolpidem.