Rapid HPLC analysis of the antiepileptic lamotrigine and its metabolites in human plasma

A liquid chromatographic method with diode array detection (DAD) has been developed for the analysis of the antiepileptic agent Lamotrigine and its metabolites, Lamotrigine 2-N-glucuronide and 2-N-methylated, in plasma samples. The analytes were separated on a C8 reversed phase column, using a mobile phase composed of methanol and a 0.45 mM, pH 3.5 phosphate buffer containing 0.17% triethylamine (24/76, v/v). Melatonin was used as the Internal Standard. The DAD detector is set at 220 nm for the detection of all the analytes. A simple protein precipitation with methanol guaranteed high extraction yield values (> 90 %) and good purification from matrix interference. Good linearity was obtained in the 0.1 – 15.0 µg/mL range for Lamotrigine and Lamotrigine 2-N-glucuronide and in the 0.1 – 2.0 µg/mL range for Lamotrigine 2-N-methylated. The analytical method was validated in terms of precision, extraction yield and accuracy. These assays gave RSD% values for precision always lower than 4.3 % and mean accuracy higher than 80 %. The method seems to be suitable for the analysis of plasma samples from patients treated with Lamictal.