Volumetric Absorptive Microsampling: A New Sampling Tool for Therapeutic Drug Monitoring of Antiepileptic Drugs

Background: Volumetric absorptive microsampling (YAMS) is a novel sampling technique for the collection of fixed-volume capillary blood. In this study, a new analytical method was developed and used to quantify 14 different antiepileptic drugs (AEDs) and 2 active metabolites in samples collected by YAMS. These data were compared with concentration measurements in plasma. Methods: The authors developed a selective and sensitive liquid chromatography-mass spectrometry (LC-MS/MS) assay to measure the concentrations of several AEDs in whole blood collected by YAMS, which were compared with a commercially available LC-MS/MS kit for AED monitoring in plasma. Drugs and internal standards were extracted from whole blood/plasma samples by a simple protein precipitation. Results: An LC-MS/MS method analyzing YAMS samples was successfully developed and validated for the determination of various AED concentrations in whole blood according to EMA guidelines for bioanalytical method validation. Extraction recovery was between 91% and 110%. No matrix effect was found. The method was linear for all drugs with R-2 >= 0.989 in all cases. Intra-assay and inter-assay reproducibility analyses demonstrated accuracy and precision within acceptance criteria. Carry over and interferences were negligible. No volumetric HCT% bias was found at 3 different HCT values (35%-55%) with recovery being consistently above 87%. Samples are very stable at temperatures ranging from -20 degrees C to 37 degrees C and for a 4-month period. Leftover EDTA samples from 133 patients were tested to determine concentration differences between plasma and whole blood sampled by YAMS. The resulting difference varied less than 15% apart from those drugs with a blood/plasma ratio (R) different from 1. Conclusions: The assay allows for highly sensitive and selective quantification of several AEDs in whole blood samples collected by YAMS. The developed method is accurate and precise and free from matrix effects and volumetric HCT% bias.