LAUSR

Background: Worldwide, approximately 50 million people live with epilepsy, a quarter of which are treated with antiepileptic drugs (AEDs). Therapeutic drug monitoring (TDM) of AEDs is often necessary to assess therapeutic compliance, potential drug-drug interactions, and pharmacokinetic interand intravariability secondary to significant differences in excretion and metabolism. TDM is necessary to minimize the destructive toxicities of AEDs including hematopoietic dysfunction, pruritus, rash, Steven-Johnson syndrome, anxiety, agitation, suicidal ideation, liver failure, gastrointestinal issues, and neurologic dysfunction. Tandem mass spectrometry with stable isotope internal standards is the gold standard for the measurement of AEDs. Here, we present a rapid ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the simultaneous measurement of gabapentin, lamotrigine, levetiracetam, monohydroxy derivative (MHD) of oxcarbazepine (the main, active oxcarbazepine metabolite, also known as licarbazepine), and zonisamide in serum. Methods: For analysis, 20 μL serum samples were added to acetonitrile in the presence of deuterated internal standards for protein precipitation. After centrifugation, 10 μL of supernatant was added to 90 μL of water. Ten μL of this solution was injected into a C18 column for reversed phase UPLC chromatographic separation. Quantification of analytes was accomplished using positive-mode electrospray ionization and collision-induced dissociation MS. Total run time was 3 minutes. Assay parameters were evaluated according to Food and Drug Administration (FDA) bioanalytical guidelines. Results: To guide our assay development, we evaluated the range of AED levels for our patient population from lab results assayed at a reference laboratory. Over the course of one year, 1,825 total samples were assayed. One levetiracetam drug level was greater than 100 ug/mL, and the lower limit of quantification (LLOQ) for all drugs analyzed ranged between 2 ug/mL and 0.2 ug/mL. Therefore, an assay range of 0.1 ug/mL to 100 ig/mL was chosen for all analytes and was linear (r2 > .999) from 0.1 ug/mL to 100 ug/mL. This assay demonstrated acceptable accuracy and precision (%DEV <20% and %CV <20% for the LLOQ, %DEV <15% and %CV <15% at all other levels tested), linearity across the reportable range (r2 > .999, slopes ranging 0.968–1.062), carryover, stability under relevant storage conditions, matrix effects, recovery, and extraction and processing efficiency in accordance with FDA guidelines. Additionally, a cross-comparison with a reference laboratory using a similar methodology was performed. Conclusions: A rapid, high-throughput, and robust UPLC-MS/MS method for monitoring multiple antiepileptics was developed and validated to address the clinical needs of our patient population.