OBJECTIVE To establish a method to simultaneously determine the plasma concentration of lacosamide(LCM) and O-desmethyl lacosamide(ODL) of children with epilepsy, which based on ultra-high performance liquid chromatography-quadrupole-electrostatic field Orbitrap mass spectrometry(UPLC-Q-Exactive-MS). Using the established method to analyze the correlation among the plasma concentration of LCM and ODL, dosage, and estimated glomerular filtration rate(eGFR). Follow-up and therapeutic drug monitoring were carried out for patients who were taking LCM.

METHODS The plasma samples were pretreated by protein precipitation method. LCM-D3 as the internal standard and the gradient elution was performed with 0.2% formic acid aqueous solution(A)-acetonitrile(B) as mobile phase at a flow rate of 0.3 mL·min⁻¹. The column temperature was 35 °C and the injection volume was 2 μL. Electrospray ion source positive ion mode was used for mass spectrometry detection. The specificity, lower limit of quantitation, standard curve, residual, accuracy, precision, extraction efficiency, matrix effect and stability of the method were investigated. Clinical plasma samples were determined using the established method, relevant data such as clinical dosage and eGFR were collected, and the correlation between data was analyzed using SPSS 26.0 software. The included patients were followed-up and the curative effect and related adverse reactions of LCM were recorded. Combined with the LCM blood concentration, the LCM medication regimen was optimized.

RESULTS The plasma concentrations of LCM and ODL showed a good linearly relationship between 0.10−40.00 μg·mL⁻¹(r>0.99), lower limit of quantitation was 0.1 μg·mL⁻¹, strong specificity, good extraction efficiency and stability, intra-and inter-batch precision RSDs≤8.65%, unaffected by normal plasma and hemolytic plasma(≤5%) matrix. The methodology verification was in accordance with the provisions of the Chinese Pharmacopoeia 2020 edition. The oral dose of LCM was respectively positively correlated with the plasma concentration of LCM(r=0.4058, P<0.0001) and ODL(r=0.3664, P<0.0001). The plasma concentration of LCM was poor positive correlation with the plasma concentration of ODL(r=0.2966, P=0.0003). The eGFR was negatively associated with the ratio of the concentration between LCM and ODL(r=−0.3902, P<0.0001). The method was used to measurement the plasma drug concentration of 142 children with epilepsy and the follow-up of 125 pediatric patients was completed, the efficacy of the drug was recorded. Analysis of LCM medication status, efficacy and adverse reactions in pediatric patients combined with LCM blood concentration. The effective rate of LCM in the treatment of epilepsy was 97.6%, and the incidence of adverse reactions was 29.6%.

CONCLUSION In this study, the isotope dilution-UPLC-Q-Exactive-MS method is established to determine LCM and ODL concentration in children's plasma. The method is rapid, simple, stable and economical, and can be applied to clinical drug monitoring and pharmacokinetic study of children treated with LCM. LCM has good efficacy in the treatment of focal seizures in children and has few adverse reactions, which is suitable for the treatment of childhood epilepsy.