Qualitative analysis of zolpidem and its metabolites M-1 to M-4 in human blood and urine using liquid chromatography–tandem mass spectrometry

Simultaneous Analysis of Zolpidem, Four Hydroxyzolpidems and Two Zolpidem Carboxylic Acids in Postmortem Urine Using Liquid Chromatography--Tandem Mass Spectrometry

Zolpidem (ZOL) is a short-acting hypnotic that is sometimes used in drug-facilitated crimes such as sexual assaults, robbery and homicides. Therefore, it is important to understand the metabolism of ZOL. This study quantified ZOL and its metabolites, including two carboxylic acids (zolpidem phenyl-4-carboxylic acid [M1] and 6-carboxylic acid [M2]) and four hydroxyzolpidems (4-(hydroxymethyl)phenyl zolpidem [M3], 6-hydroxymethyl zolpidem [M4], 7-hydroxyzolpidem [7OH] and 8-hydroxyzolpidem [8OH]) in postmortem urine using liquid chromatography--triple quadrupole mass spectrometry. The concentration of M1 was highest in all cases, followed by total 7OH in five of six samples. The concentrations of M2 and total M4 were relatively high. Most of M4 and 8OH were excreted as conjugates, whereas up to 55% of 7OH was excreted in its free form. Peaks corresponding to zolpidem dihydrodiol (ZHDH), dihydro(hydroxy)zolpidem cysteine adduct (DHZCys) and zolpidem cysteine adduct (ZCys) were also detected in all the urine samples. ZDHD was excreted as conjugates, whereas almost all DHZCys and ZCys were in their free form.

Qualitative analysis of 7- and 8-hydroxyzolpidem and discovery of novel zolpidem metabolites in postmortem urine using liquid chromatography-tandem mass spectrometry

PURPOSE

Zolpidem (ZOL) is a hypnotic sometimes used in drug-facilitated crimes. Understanding ZOL metabolism is important for proving ZOL intake. In this study, we synthesized standards of hydroxyzolpidems with a hydroxy group attached to the pyridine ring and analyzed them to prove their presence in postmortem urine. We also searched for novel ZOL metabolites in the urine sample using liquid chromatography-triple quadrupole mass spectrometry (LC-QqQMS) and liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QqTOFMS).

METHODS

7- and 8-Hydroxyzolpidem (7OHZ and 8OHZ, respectively) were synthesized and analyzed using LC-QqQMS. Retention times were compared between the synthetic standards and extracts of postmortem urine. To search for novel ZOL metabolites, first, the urine extract was analyzed with data-dependent acquisition, and the peaks showing the characteristic fragmentation pattern of ZOL were selected. Second, product ion spectra of these peaks at various collision energies were acquired and fragments that could be used for multiple reaction monitoring (MRM) were chosen. Finally, MRM parameters were optimized using the urine extract. These peaks were also analyzed using LC-QqTOFMS.

RESULTS

The presence of 7OHZ and 8OHZ in urine was confirmed. The highest peak among hydroxyzolpidems was assigned to 7OHZ. The novel metabolites found were zolpidem dihydrodiol and its glucuronides, cysteine adducts of ZOL and dihydro(hydroxy)zolpidem, and glucuronides of hydroxyzolpidems.

CONCLUSIONS

The presence of novel metabolites revealed new metabolic pathways, which involve formation of an epoxide on the pyridine ring as an intermediate.