Background: Lamotrigine (LTG), topiramate (TPM) and oxcarbazepine (OXC) are commonly used antiepileptic drugs. The bioactivity and toxicity of these drugs was related to their blood concentrations which varied greatly among individuals and required to be monitored for dose adjustment. However, the commercial method for monitoring of these drugs is not available in China.
Methods: A UHPLC-MS/MS method for simultaneous determination of LTG, TPM, OXC and OXC active metabolite (10,11-dihydro-10-hydroxycarbazepine, MHD) was developed and validated according to the guidelines and applied in clinical practice.
Results: The separation was achieved by using methanol and water (both contain 0.1% formic acid) at 0.4 mL/min under gradient elution within 3 min. For all analytes, the isotope internal standard was used; the selectivity was good without significant carry over; LTG and TPM were linear between 0.06 to 12 mg/L while OXC and MHD were linear between 0.03 to 6 mg/L, the upper limit could be 10-fold higher because 10-fold dilution with water did not affect the results; the intra-day and inter-day bias and imprecision were –13.11% to 5.42% and < 13.32%; the internal standard normalized recovery and matrix factor were 90.95% to 111.94% and 95.57% to 109.91%; and all analytes were stable under tested conditions. LTG and OXC-D4 shared two ion pairs m/z 257.1 > 212.0 and 257.1 > 184.0, and m/z 257.1 > 240.0 was suggested for OXC-D4 quantitation. Lamotrigine and lamotrigine-13C3 shared three ion pairs m/z 259.0 > 214.0, 259.0 > 168.0 and 259.0 > 159.0, and m/z 259.0 > 144.9 was suggested for LTG-13C3 quantitation. CBZ had a slight influence on OXC analysis only at 0.225 mg/L (bias, 20.24%) but did not affect MHD analysis. Optimization of chromatography conditions was useful to avoid the influence of isobaric mass transitions on analysis. This method has been successfully applied in 208 patients with epilepsy for dose adjustment.
Conclusions: An accurate, robust, rapid and simple method for simultaneous determination of LTG, TPM, OXC, and MHD by UHPLC-MS/MS was developed, validated and successfully applied in patients with epilepsy for dose adjustment. The experiences during method development, validation and application might be helpful for other researchers.