Highly sensitive LC-MS/MS-ESI method for determination of phenelzine in human plasma and its application to a human pharmacokinetic study

A selective, sensitive and rapid LC-MS/MS method has been developed and validated for quantification of the phenelzine (PZ) in 200 μL of human plasma using hydroxyzine (HZ) as an internal standard (IS) as per regulatory guidelines. The sample preparation involved the derivatization of PZ using pentaflurobenzaldehyde followed by solid phase extraction process to extract PZ and HZ from human plasma. LC-MS/MS was operated under the multiple reaction-monitoring mode (MRM) using the electro spray ionization technique in positive ion mode and the transitions of m/z 305.1 → 105.1 and m/z 375.3 → 201.1 were used to measure the derivative of PZ and IS, respectively. The total run time was 3.5 min and the elution of PZ and HZ occurred at 2.53, and 1.92 min, respectively; this was achieved with a mobile phase consisting of 10 mM ammonium acetate: acetonitrile (20:80, v/v) at a flow rate of 1.0 mL/min on an Ace C18 column with a split ratio of 70:30. The developed method was validated in human plasma with a lower limit of quantitation 0.51 ng/mL. A linear response function was established for the range of concentrations 0.51-25.2 ng/mL (r > 0.995) for PZ. The intra- and inter-day precision values met the acceptance criteria. PZ was stable in the battery of stability studies viz., stock solution, bench-top, auto-sampler, long-term and freeze/thaw cycles. The developed assay method was applied to an oral bioequivalence study in humans.