Determination of gabapentin in plasma by high-performance liquid chromatography

A rapid and simple method for determination of the novel antiepileptic compound gabapentin [1-(aminomethyl)cyclohexaneacetic acid] in plasma is described. Blank human plasma was spiked with gabapentin (1.0-10.0 mu g/ml) and internal standard [1-(aminomethyl)-cycloheptaneacetic acid; 5.0 mu g/ml]. Individual samples were treated with 2 M perchloric acid, centrifuged and then derivatised with o-phthalaldehyde-3-mercaptopropionic acid. Separation was achieved on a Beekman Ultrasphere 5 mu m reversed-phase column with mobile phase consisting of 0.33 M acetate buffer (pH 3.7; containing 100 mg/l EDTA)-methanol-acetonitrile (40:30:30, v/v). Eluents were monitored by fluorescence spectroscopy with excitation and emission wavelengths of 330 and 440 nm, respectively. The calibration curve for gabapentin in plasma was linear (r=0.9997) over the concentration range 1.0-10.0 mu g/ml. Recovery was seen to be greater than or equal to 90%. The inter- and intra-assay variations for three different gabapentin concentrations were less than or equal to 10% throughout. The lower limit of quantitation was found to be 0.5 mu g/ml. Chromatography was unaffected by a range of commonly employed antiepileptic drugs or selected amino acids.