Metabolite ratios and detection times in urine following a single dose of zopiclone

Zopiclone (ZOP) is a Z-drug that features prevalently in impaired driving, petty drug offenses or drug-facilitated sexual assault cases. Additional characterization of ZOP urinary pharmacokinetics would support its interpretation in forensic casework. This study aimed to determine the detection windows and excretion patterns of ZOP, zopiclone-N-oxide (ZOP-NO), and N-desmethylzopiclone (N-DMZOP) in urine, and evaluate the utility of metabolite ratios for predicting the time of last ZOP intake. Subjects (n=16) received a single oral dose of either 5 mg or 10 mg Imovane®, and urine samples were collected pre-dosing, at 2, 4, 6, 8, 10, 12, 14, and 24 hours on day 1, and on days 2, 3, 4, 5, 6, 10, and 14 post-dose. ZOP, ZOP-NO, N-DMZOP, and the degradation product 2-amino-5-chloropyridine (ACP) were quantified using LC-MS/MS. Although T_max of all three analytes did not differ significantly between dosing groups, the 10 mg group produced significantly higher C_max concentrations of N-DMZOP compared to the 5 mg group, with insignificant differences in the C_max of ZOP and ZOP-NO. The ratio of N-DMZOP/ZOP-NO showed a relationship to the time of intake, but predictions were underestimated possibly due to the small sample size, inter-individual differences, and to some degree, by the degradation of zopiclone metabolites prior to analysis. These findings highlight the need to include ACP in ZOP to improve the interpretation of ZOP and metabolite concentrations in forensic casework. Notably, N-DMZOP displayed the longest detection window compared to ZOP and ZOP-NO, highlighting its utility as a biomarker for extended detection of ZOP intake.