By: William Johnson
Webster's online dictionary defines insomnia as “prolonged and usually abnormal inability to obtain adequate sleep”. Zolpidem has been prescribed for insomnia since 1986 in Europe (StilnochtTM) and since 1996 in the United States (AmbienTM). Classified as a non-benzodiazepine sedative hypnotic, zolpidem provides short-term insomnia relief in 5 and 10 mg doses. Designed to provide 8 hours of uninterrupted sleep, zolpidem has a rapid onset of effects and a relatively short half life (T1/2).
While structurally unrelated to the benzodiazepines, zolpidem also acts on the GABAA receptor, leading to central nervous system (CNS) depression. For this reason, users are cautioned to avoid operating heavy machinery or automobiles following zolpidem administration. Driving impairment caused by zolpidem is similar to that of ethanol and other CNS depressants, with negative effects on vision, speech and balance/coordination. Notable symptoms of zolpidem impairment can include a penetrating/glassy stare, extremely poor balance with noted sway, no sense of surroundings, unusually slow and quiet speech, memory impairment, unusually slow driving speeds and driving into stationary objects. Drug Recognition Expert (DRE) officers have observed impairment consistent with the CNS depressants.
A review of Wisconsin 's Operating While Intoxicated (OWI) casework from 1999-2004* detected zolpidem in 187 (males = 107, females = 80) of 8121 blood specimens tested for ethanol and drugs. Sixty-five percent of positive zolpidem cases were from drivers between 31-50 years of age.
Zolpidem was the only substance detected in 21 of these cases (males = 15, females = 6). In 57% of the zolpidem only cases, blood concentrations were in excess of expected single dose serum peak concentrations (290-1200 ng/mL). The overall number of specimens with elevated zolpidem levels is indicative of the abuse potential of this medication. Regardless of concentration, one would not expect to find zolpidem in the blood of drivers if taken as directed.
There have been reports of unusual behaviors of “sleep-eating” and “sleep-driving” from patients allegedly taking zolpidem as prescribed. These individuals apparently do not maintain a deep sleep and appear unaware of their odd behavior. The time release formulation, Ambien CRTM, may address the issue by providing both rapid and sustained sleep to individuals.
*W. Johnson, P. Harding, A. Cochems, L. Liddicoat, “Zolpidem Impaired Drivers in Wisconsin - A Six Year Retrospective,” Society of Forensic Toxicologists, Inc. Annual Meeting 2005.
Editor's Note: William Johnson is an Advanced Chemist for the Wisconsin State Laboratory of Hygiene – Toxicology Section.
Driving impairment caused by zolpidem is similar to that of ethanol and other CNS depressants, with negative effects on vision, speech and balance/coordination.
Zolpidem at a glance |
Use |
Short term relief of insomnia |
Formulations/Dosage |
Ambien TM (5 or 10 mg) & Ambien CR TM (6.25 or 12.5 mg) |
Peak serum concentration |
29 – 272 ng/mL (achieved 1.5 – 2.5 hours post ingestion) |
Half life (T 1/2 ) |
1.4 – 4.5 hours |
Duration of effect |
Up to 8 hours as prescribed |
Drug Classification |
Central Nervous System (CNS) depressant |
Analysis |
Alkaline liquid:liquid extraction and acid back extraction, analyzed by Gas Chromatography with Nitrogen Phosphorus (NPD) or Mass Selective (MSD) detection. |
Zolpidem OnlY: Driving |
Hit stationary objects
(light poles preferred) |
52%
28% |
Speed: well below posted limits
Above posted limits |
38%
10% |
Lane deviation |
52% |
Tires over curb/ on sidewalk |
33% |
Hitting another vehicle |
24% |
Driving into ditch |
19% |
Driving wrong direction |
14% |
