New micromethod for the determination of lamotrigine in human plasma by high-performance liquid chromatography.

An extraction procedure and reversed-phase high-performance liquid chromatographic assay is described and validated for the determination of lamotrigine in human plasma. The method involves extraction with chloroform-isopropanol after alkalinization with a carbonate buffer, back-extraction into 0.05% phosphoric acid and separation by reversed-phase HPLC using a 5-micron Supelco diphenyl column (150 x 4.6 mm I.D.). Quantitation was performed by measurement of the UV absorbance at a wavelength of 265 nm. This method was carried out on 50-200 microliters samples of plasma, depending on whether they were pediatric or adult samples. The lower limit of quantitation was 0.2 microgram/ml using 200 microliters of plasma. A linear response was tested from 0.5 to 20 micrograms/ml. Within- and between-day accuracy and precision were always below 10.0% at all analysed concentrations. The method selectivity towards the most used antiepileptic drugs has been proven. Satisfactory performances were obtained in the evaluation of samples from epileptic patients.