Solid-Phase Extraction Study and RP-HPLC Analysis of Lamotrigine in Human Biological Fluids and in Antiepileptic Tablet Formulations

An efficient off-line solid-phase extraction (SPE) of lamotrigine, 3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine (LTG), a new antiepileptic drug, from human serum and urine, prior to high-performance liquid chromatographic analysis, was tested and optimized. High extraction recoveries were achieved from C 8 Bond Elut cartridges (200mg/3ml), using acidic acetonitrile for the elution of LTG and the internal standard, 3,5-diamino-6-(2-methoxyphenyl)-1,2,4-triazine. Isocratic reversed-phase high-performance liquid chromatographic (RP-HPLC) analysis on octylsilica, using a Lichrosorb RP-8, 5μm, 250x4.6 mm i.d. column and a mobile phase consisting of 0.05M acetate buffer pH5.6 and acetonitrile (72:28 v/v) proved to be sensitive and rapid. The identification of LTG was performed by UV detection at 306nm. The method detects approximately 0.9 ng of LTG on-column, using a 20-μl loop, and linearity holds from approximately 0.044 to 7.8 μg/ml in standard solutions. In plasma and urine, the limits of detection are 1.1 and 1.2ng respectively, while linearity holds from approximately 0.087 to 3.49μg/ml. The proposed method was also used for the direct analysis of antiepileptic tablets.