Validated LC-MS-MS method for the determination of gabapentin in human plasma: application to a bioequivalence study

A simple and rapid liquid chromatography-tandem mass spectrometric method is developed and validated for the determination of gabapentin in human plasma. Metformin is used as an internal standard. The method utilizes protein precipitation with acetonitrile followed by separation on a C(8) column using 10 mM ammonium formate buffer pH 3.0 and acetonitrile as mobile phase. Detection was performed on a quadrupole mass spectrometer using an electrospray ionization interface in selected reaction monitoring mode. The method proves to be specific, sensitive, accurate, precise, and linear over the concentration range of 50-5000 ng/mL with correlation coefficients greater than 0.99. The lower limit of quantification for gabapentin is 50 ng/mL using a 200-microL plasma sample. Intra- and inter-day precisions are less than 8.4% whereas accuracies are within 10.2%. The method is successfully applied to a bioequivalence study of gabapentin in 24 healthy volunteers.