Determination of nalmefene by high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry

Nalmefene is an opioid antagonist used in the treatment of alcoholism and opioid overdose. A highly sensitive method was developed to measure nalmefene in human and rabbit plasma and rabbit serum. Nalbuphine was used as internal standard. Liquid-liquid extraction was applied using n-butyl chloride/acetonitrile (4:1). High-performance liquid chromatography interfaced by electrospray ionization to a tandem mass spectrometer was used for quantitation. Primary validation experiments were conducted using human plasma then it was cross-validated in rabbit plasma and rabbit serum. Specificity (peak-area ratio of blank plasma or serum to its internal standard as percent of peak-area ratio of blank plasma or serum fortified with 0.1 ng/mL nalmefene to its internal standard) ranged from 2.09 to 5.29 with a mean of 3.21% for human plasma and from 4.08 to 6.63 with a mean of 5.55% for rabbit plasma and from 2.47 to 6.17 with a mean of 3.62% for rabbit serum. The mean recovery for nalmefene was 80% in human plasma. The calibration range was from 0.1 to 100 ng/mL. Intrarun accuracy of the lower limit of quantitation (0.1 ng/mL) in all matrices was within 18.0% of target with intrarun precision within 13.6%. At 0.3, 35, and 75 ng/mL, the intrarun accuracy in all matrices was within 11.9% of target with intrarun precision within 6.6%. The inter-run accuracy in human plasma was within 8.0% of target with inter-run precision within 6.6%. Nalmefene was stable in human and rabbit plasma and rabbit serum for up to 24 h at room temperature and in human plasma after three freeze-thaw cycles. Following intravenous injection of 5 mg/kg nalmefene to rabbits, the mean area under curve for 0 to 24 h was 1116 (ng)(mL)(-1)(h), and the mean plasma clearance was 67.9 (mL)(min)(-1)(kg)(-1).