Zopiclone is a nonbenzodiazepine hypnotic agent used in the treatment of insomnia. It is a cyclopyrrolone, which increases the normal transmission of the neurotransmitter gamma-aminobutyric acid in the central nervous system, as benzodiazepines do, but in a different way. Zopiclone is indicated for the short-term treatment of insomnia where sleep initiation or sleep maintenance are prominent symptoms. Long-term use is not recommended, as tolerance, dependence, and addiction can occur with prolonged use. Zopiclone is partly extensively metabolized in the liver to form an active N-demethylated derivative (N-desmethylzopiclone) and an inactive zopiclone-N-oxide.
In urine, the N-demethyl and N-oxide metabolites account for 30% of the initial dose. Between 7 and 10% of zopiclone is recovered from the urine, indicating extensive metabolism of the drug before excretion. The terminal elimination half-life of zopiclone ranges from 3.5 to 6.5 hours (5 hours on average). Time to peak plasma concentration is 1 – 2 h, the absorption rate constant is 1.3 h-1 and maximum plasma concentration after administration of 7.5 mg is 131µg/l.
Zopiclone may be measured in blood, plasma, or urine by chromatographic methods. Plasma concentrations are typically less than 100μg/l during therapeutic use, but frequently exceed 100μg/l in automotive vehicle operators arrested for impaired driving ability and may exceed 1000μg/l in acutely poisoned patients. Post mortem blood concentrations are usually in a range of 0.4-3.9 mg/l in victims of fatal acute overdose.
The Multi-Drug Rapid Test Panel yields a positive result when the concentration of Zopiclone in urine exceeds detective level.