A RAPID AND SPECIFIC ASSAY FOR THE DETERMINATION OF LAMOTRIGINE IN HUMAN PLASMA BY NORMAL-PHASE HPLC

A rapid and specific high-performance liquid chromatography assay of l amotrigine in human plasma is described. Lamotrigine is extracted with dichloromethane from buffered plasma to which an internal standard ha s been added. The solvent is directly injected into a 250 x 4.6-mm Sph erisorb Silica column and the drug is eluted by using a mixture of met hanol, n-heptane, dichloromethane, and 28-30% ammonium hydroxide (20:4 0:40:0.3 vol/vol) at a flow rate of 1 ml/min. The eluates are detected at 240 nm. The assay requires 250 mu l of sample, and concentrations as low as 0.4 mu g/ml can be measured accurately. The method is linear in the range of 0.4-16 mu g/ml, with a mean coefficient of correlatio n (r) greater than or equal to 0.997. Within-and between-day relative standard deviations at three different concentration levels (1, 4, and 8 mu g/ml) are less than or equal to 8.6%.