New high-performance liquid chromatographic method for plasma/serum analysis of lamotrigine

Lamotrigine is an anticonvulsant drug recently approved in Italy for clinical use. Therapeutic monitoring of lamotrigine is relevant for patient management and avoidance of toxicity. The authors describe a simple, sensitive, and highly selective high-performance liquid chromatography method that does not involved extraction for analysis of serum lamotrigine. Serum (20 muL) with internal standard (BW 725 C) was injected directly into a column (25 cm x 4.6 mm) with an internal surface reversed phase (ISRP). The mobile phase consisted of 0.01 mol/L potassium phosphate bibasic (pH 6.0) and acetonitrile (82:18), the flow rate was 1.0 mL/min, and UV detection was optimized at 330 nm. The overall between-run coefficient of variance ranged from 1.89% to 3.25% and the lowest limit of detection was 0.05 mg/L. High linearity (r = 0.9996) in a wide range of concentrations (0.1-20.0 mg/L) and no interference with other antiepileptic drugs, benzodiazepines, and tricyclic antidepressants were the other characteristics of the method. The innovation of this method is the use of ISRP column and the choice of detection wavelength, which allow a shorter analysis time (5-6 minutes). The possibility of direct injection of plasma samples into the column permits a reduction in reagent consumption and in analytic steps, and hence in analytic error.