Development and application of an LC-MS/MS method for 8 antiepileptic drugs and 2 metabolites using microsampling techniques (DBS and VAMS).

Therapeutic drug monitoring (TDM) of antiepileptic drugs (AEDs) is used for optimization and individualization of patients' treatment. Capillary microsampling techniques are a promising alternative to conventional venous sampling for TDM. Both dried blood spots (DBS) and volumetric adsorptive microsampling (VAMS) devices are less invasive and patient-friendly sampling techniques which have been gaining interest in the last years. This study describes the development and validation of an LC-MS/MS method for the determination of 8 AEDs (Carbamazepine, Lacosamide, Levetiracetam, Lamotrigine, Phenobarbital, Valproic acid) and 2 metabolites (10,11-Dihydro-10-hydroxy-carbamazepine (DHCB) and carbamazepine-10,11-epoxide) in DBS and VAMS samples. The method was fully validated for linearity, selectivity, accuracy, precision, carryover, matrix effect, recovery and stability (15 days at room temperature and 72 h in autosampler). Moreover, the volume effect, volcano effect, and the hematocrit (Hct) effect were also assessed for DBS samples. All parameters showed satisfactory results, with a limit of quantification ranging from 0.5 to 10 µg/mL, depending on the analyte. Some instability issues were detected in DBS samples for oxcarbazepine. However, the inclusion of oxcarbazepine's metabolite DHCB overcomes this problem as it was stable under both conditions tested. Moreover, this is the first DBS or VAMS method reporting the inclusion of DHCB, which seems essential for the TDM of oxcarbazepine. The method was applied to 80 paired samples from patients under treatment with these drugs in order to study the suitability of the method for the detection of these compounds, and compare concentrations in paired VAMS, DBS, whole blood and plasma samples. Ratios between paired samples show a promising correlation between microsampling techniques and plasma concentrations.