DETERMINATION OF ANTIBIOTIC FOSFOMYCIN IN CHICKEN SERUM BY LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY

A high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed for the determination of fosfomycin in chicken serum using fudosteine as the internal standard. Serum samples were treated with methanol to precipitate proteins. A subsequent clean up using liquid-liquid extraction followed by dilution was performed to eliminate phospholipids which are prone to produce unwanted matrix effects. The HPLC-MS/MS system involved the use of an isocratic mobile phase on a cyano stationary phase column and electrospray ion source operating in negative ion mode. Single reaction monitoring of transitions m/z 137 79 and 178 91 was performed on a triple quadrupole mass spectrometer to quantify fosfomycin and fudosteine, respectively. Response was linear over the range of 0.1 to 50gmL-1. Recovery ranged from 95 to 108%. Accuracy determined for spiked samples at 5, 10, and 20gmL-1 was -7.8, 1 and -0.7%, respectively, expressed as relative error. Within day and between days precision, in terms of coefficient of variation, were less than 10% for all concentrations. The developed method was successfully used in a pharmacokinetic study after oral administration of calcium fosfomycin to broiler chickens.