Eszopiclone, a non-benzodiazepine hypnotic agent, is a pyrrolopyrazine derivative of the cyclopyrrolone class. It is the (S)-configuration isomer of zopi-clone (Imovane™, Aventis), a hypnotic agent that has been available in Europe since 1987. Eszopiclone is a white to light-yellow crystalline solid. According to the manufacturer, it is very slightly soluble in water, slightly soluble in ethanol, and soluble in phosphate buffer. It is available as film-coated tablets in dosages of 1, 2, and 3 mg.
MECHANISM OF ACTION
Although the exact mechanism of action of eszopiclone is unknown, its hypnotic effect is thought to result from its interaction with the gamma-amino-butyric acid (GABA) receptor at receptors close to or allosterically coupled to the benzodiazepine receptor.
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Absorption and Distribution
Eszopiclone is rapidly absorbed after oral administration. According to the manufacturer, the peak plasma (Cmax) and time to maximum concentrations (Tmax) are achieved within one hour after oral administration. The plasma protein-binding property for eszopiclone is weak, with only 52% to 59% being protein-bound. As a result of this weak protein binding, drug-drug interactions caused by protein binding should not occur, and none have been reported. Administration of eszopiclone after a high-fat meal results in a reduction of the Cmax by 21% and in a delay of one hour for the Tmax. However, no change in the area-under-the-curve (AUC) concentration has been observed.
Metabolism and Elimination
Eszopiclone is metabolized by oxidation and demethylation into (S)-zopi-clone-N-oxide and (S)-^-desmethyl-zopiclone. The latter compound retains some potency in binding to GABA receptors, but its potency is substantially lower than that of eszopiclone. The former compound shows no significant binding to the GABA receptor. The cytochrome isoenzymes CYP450 3A4 and CYP450 2E1 are also involved in eszopiclone metabolism, as shown in in vitro studies. Extra monitoring is necessary when eszopiclone is administered with a CYP3A4 inhibitor or inducer.
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Eszopiclone does not appear to have any CYP450 inhibitory properties. Its half-life is approximately six hours. Less than 10% of the orally administered eszopiclone dose is excreted in the urine as the parent drug.