Determination of zolpidem in serum microsamples by high-performance liquid chromatography and its application to pharmacokinetics in rats.

A single-solvent extraction step high-performance liquid chromatographic method is described for quantitating zolpidem in rat serum microsamples (50 microl). The separation used a 2.1 mm I.D. reversed-phase OD-5-100 C18 column, 5 microm particle size with an isocratic mobile phase consisting of methanol-acetonitrile-26 mM sodium acetate buffer (adjusted to pH 2.0 with 40% phosphoric acid) containing 0.26 mM tetrabutylammonium phosphate (13:10:77, v/v/v). The detection limit was 3 ng/ml for zolpidem using an ultraviolet detector operated at 240 nm. The recovery was greater than 87% with analysis performed in 12 min. The method is simple, rapid, and applicable to pharmacokinetic studies of zolpidem after administering two intravenous bolus doses (1 and 4 mg/kg) in rats.