A rapid liquid chromatographic method for the determination of lamotrigine in plasma

A rapid sensitive and simple high-performance liquid chromatographic (HPLC) method for the determination of lamotrigine in plasma is described. The drug was extracted from 100 microliters of plasma with chloroform:isopropanol (95:5% v/v) in the presence of 100 microliters of phosphate buffer (10 mM). The extract was evaporated and the residue was reconstituted with mobile phase and injected onto the HPLC system. The drug and the internal standard (chloramphenicol) were eluted from a Symmetry C18 stainless steel column at ambient temperature with a mobile phase consisting of 0.01 M potassium-acetonitrile-methanol (70.20:10% v/v/v), adjusted to pH 6.7, at a flow rate of 1.3 ml min-1 and the detector was monitored at 214 nm. Quantitation was achieved by measurement of the peak-area ratio of the drug to the internal standard and the lower limit of detection for lamotrigine in plasma was 20 ng ml-1. The intraday precision ranged from 3.34 to 6.12% coefficient of variation (CV) and the interday precision ranged from 2.15 to 8.34% CV. The absolute and relative recoveries of lamotrigine ranged from 86.93 to 90.71% and from 95.18 to 107.13%, respectively. The method was applied in studying the pharmacokinetics of lamotrigine administered orally to rabbits. This reliable micro-method would have application in pharmacokinetic studies of lamotrigine where only small sample sizes are available, e.g. paediatric patients.