Liquid Chromatography–Tandem Mass Spectrometry Work Flow for Parallel Quantification of Methotrexate and Other Immunosuppressants

[摘要] To the Editor:Methotrexate is a potentially toxic folic acid antagonist that is widely used as an immunosuppressant and chemotherapeutic agent. After high doses (0.035–12 g/m2) are administered, methotrexate concentrations in the plasma or serum are carefully monitored so that the patient can be rescued, if necessary, with the proper dose of leucovorin, a folic acid analog that bypasses the important enzymes inhibited by methotrexate (1).Recently, the manufacturer of the fluorescence polarization immunoassay we use for monitoring (TDX platform; Abbott Laboratories) announced its intention to move the assay to a different proprietary platform. In addition, the immunoassay is known to be nonspecific. For example, the assay strongly cross-reacts with diamino- N 10-methylpteroic acid, a minor (<5%) endogenous methotrexate metabolite and the major (>98%) product of pharmacologic inactivation of methotrexate with carboxypeptidase G2 (2). As an alternative to reagent-dependent proprietary methods, a liquid chromatography–tandem mass spectrometry (LC-MS/MS) method, with an improved specificity, can be used to measure methotrexate (2, 3).Many laboratories, including our own, have replaced immunoassays for other immunosuppressants, which can also suffer from interferences, with laboratory-developed tests that use LC-MS/MS (4). In contrast to methotrexate, the number of samples processed for other immunosuppressants with the immunosuppressant assay is high enough to support the LC-MS/MS infrastructure in …

[学科分类] 过敏症与临床免疫学