Simultaneous Determination of Pethidine and Atropine in Rabbit Plasma by LC-MS-MS and Its Application to a Pharmacokinetic Study after Intramuscular Administration

A sensitive and selective liquid chromatography-tandem mass spectrometry method for the determination of pethidine and atropine in rabbit plasma was developed and validated. The analytes and internal standard (IS) are extracted from plasma by liquid-liquid extraction using ethyl acetate, and separated on a Zorbax SB-Aq column (2.1 x 150 mm, 3.5 mu m) using acetonitrile-0.1% formic acid as mobile phase with gradient elution. Electrospray ionization source was applied and operated in positive ion mode, and multiple reaction monitoring mode was used for quantification using target fragment ions m/z 247.8 -> 219.7 for pethidine, m/z 289.9 -> 123.8 for atropine and m/z 295.0 -> 266.8 for IS, respectively. The assay is linear over the range of 5-1,000 ng mL(-1) for pethidine and atropine, with a lower limit of quantification of 3 ng mL(-1) for pethidine and 5 ng mL(-1) for atropine. Intra-day and inter-day precision are less than 11% and the accuracy are in the range of 90.4-106.3%. Furthermore, the newly developed method is successfully used for the determination of pethidine and atropine in rabbit plasma for pharmacokinetic study.