MSACL 2024 Abstract

Introduction: Levetiracetam and lamotrigine are antiepileptic drugs used in the treatment of tonic-clonic seizures but require monitoring due to their narrow therapeutic ranges. Traditional monitoring methods utilize serum samples, requiring frequent venipunctures for patients. Dried blood spots (DBS) are an alternative specimen type which can easily be collected at home. However, DBS require laborious sample preparation before measurements using LC-MS/MS, limiting their use in high test volume laboratories. Herein we report a novel LC-MS/MS method that allows for the coincidental quantification of levetiracetam and lamotrigine from DBS utilizing direct inline flow through desorption technology which requires no sample preparation.

Objective: The goal of this study was to validate an LC-MS/MS method utilizing inline flow-through desorption technology to quantify levetiracetam and lamotrigine from DBS samples.

Methods: DBS were prepared by spiking bovine whole blood with levetiracetam and lamotrigine and depositing these mixtures onto dried matrix cards. Direct inline matrix desorption and chromatographic separation were achieved using a Thermo Scientific DSX-1 equipped with a Vanquish HPLC system. Samples were purified online using a Cyclone-P (1 x 50 mm) TurboFlow column and then eluted onto an Accucore™ aQ (3 x 150 mm) analytical column for further chemical separation. The HPLC was coupled to a Thermo Scientific TSQ Altis Plus triple quadrupole mass spectrometer for ion selection and detection. Sample quantification was performed using isotopically labeled internal standards and by comparison to an external calibration curve. Each batch contained five calibrators with concentrations across the linear range. Twenty runs over the course of ten days were used to determine accuracy and precision.

Results: Calibration curves for both anticonvulsants maintained a linear response (R2>0.99) which encompassed their respective therapeutic windows. Within-run precision varied with %CVs of 3.6-7.8% and between-run precision varied with %CVs of 4.5-9.7% for both drugs. Passing-Bablok regression analysis of accuracy studies revealed excellent correlations (R2=0.99) for both drugs. Our method yielded a 14-day mean difference in concentration <±20% and <±10% compared to their originally measured concentration for levetiracetam and lamotrigine, respectively, indicating that the DBS are stable for at least 14 days.

Conclusions: Automatic flow through desorption technology in tandem with LC-MS/MS can accurately and precisely quantify levetiracetam and lamotrigine from DBS samples. This investigation bolsters the number of analytes that are amenable to DBS desorption LC-MS/MS analysis, highlighting the versatility of this technology for high throughput laboratories. Furthermore, the utilization of DBS versus serum has the potential to benefit patients undergoing long-term therapeutic drug monitoring.