Sarina Yang (Presenter)
Quest Diagnostics Nichols Institute of Valencia
Bio: Dr. Sarina Yang is a scientific director of Toxicology and Special Chemistry at Quest Diagnostics Nichols Institute of Valencia. She received her Bachelor of Medicine degree from Peking University Health Science Center and PhD in Neuroscience from Northwestern University. She was trained as a clinical chemistry fellow with Drs. Alan Wu and Kara Lynch at University of California San Francisco. Dr. Yang is certified in both clinical chemistry and toxicological chemistry by the American Board of Clinical Chemistry and is a fellow of the National Academy of Clinical Biochemistry. She has also obtained the California Clinical Chemistry license and New York certificate of quantification. Dr. Yang’s research focuses on pain management and therapeutic drug monitoring using LC-MS/MS, as well as trace element testing using ICPMS.
Authorship: He Sarina Yang, Karin Thomassian, Anita Dermartirosian
Quest Diagnostics Nichols Institute of Valencia
Therapeutic drug monitoring (TDM) of the newer generation of anticonvulsant drugs (AEDs) is of great importance in treatment of seizure disorders and prevention of adverse effects. Automated immunoassay is only available for some of the newer AEDs, and antibodies used in these methods have cross-reactivity with drug metabolites, causing overestimation of concentration. We report the development and validation of a lacosamide LC-MS/MS assay as an example of a procedure for specific and accurate measurement of the newer AEDs in blood. Sensitivity, linearity, precision, accuracy, comparison of different specimen types, extracted specimen stability, and interference were validated for this assay.
In the last 20 years, 14 so-called new-generation antiepileptics drugs (AEDs) have entered the market, including eslicarbazepine, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin, and zonisamide (1). Compared to the first generation AEDs, the newer agents generally have wider therapeutic ranges and fewer serious adverse effects. However, the pharmacokinetics of the new AEDs shows significant inter-individual variability due to sex, age, race, hepatic metabolism, renal function and concomitant medications (1). Therapeutic drug monitoring (TDM) is of particular importance in the clinical management of AED therapy, as therapeutic and toxic effects of AEDs have been found to be related to serum concentration (2). TDM of new generation AEDs can benefit the treatment of seizure disorders and prevention of adverse drug effects by aiding with individualization of therapy, adjusting for variable or nonlinear pharmacokinetics, and managing special population such as pregnant women. In addition, clinicians rely upon TDM to assess patient compliance and to prevent drug misuse, particularly in patients with psychiatric disorders (3). However, automated immunoassays are only available for some of the newer generation AEDs, and antibodies used in these methods have some level of cross-reactivity with their metabolites, resulting in overestimation of drug concentration. Liquid chromatography-tandem mass spectrometer (LC-MS/MS) provides a sensitive and specific measurement of AEDs. In this study, lacosamide LC-MS/MS analysis is used as an example of a procedure for quantifying new generation AEDs in serum or plasma.
100 µL of plasma or serum specimens, calibrators, and 2 levels of custom-made UTAK AED II quality controls (5 and 12 µg/mL) were spiked with 20 µL of internal standard (lacosamide-13C, D3, 5 µg/mL). Specimen is extracted by protein precipitation using 200 µL of methanol. The mixture was vortexed for 5 minutes, and then centrifuged for 10 min at 4°C. The supernatant (150 µL) was transferred into autosampler vials. The HPLC system automatically injected 10 ìL aliquot into a Restek guard column followed by a Pinnacle DB biphenyl analytical column. The column was maintained at room temperature with a gradient elution flow rate of 0.75 mL/min. Mobile phase A consisted of 0.1% formic acid in water, and mobile phase B consisted of 0.1% formic acid in methanol. The analyte was eluted in a gradient from 10% to 90% mobile phase B. A Sciex 3200 mass spectrometer was used with a positive mode electrospray ionization source. Multiple reaction monitoring (MRM) mass spectrometry was used to monitor 2 characteristic transitions for lacosamide and 1 transition for the internal standard. Validation of the final method included determining the following characteristics by standard laboratory methods: limit of quantification (LOQ), linearity, precision, accuracy, comparison of different specimen types, extracted specimen stability, and interference by hemoglobin, triglycerides, and bilirubin.
A 7-point calibration curve exhibited consistent linearity and reproducibility in the range of 0.5 to 20 µg/mL with regression coefficient (r) > 0.99. The LOQ of lacosamide was 0.5 ìg/mL with a CV < 20%. A precision study over a 2-month period (n = 140) yielded a CV of 5.2% and 5.5% for low and high levels of controls, respectively. The accuracy study was carried out by correlating 102 sample results, including 19 send-out samples and 83 spiked samples across the concentration range of 0.5 to 20 ìg/mL. Deming regression showed a correlation coefficient of 0.989 and no bias (intercept = 0.03). Specimen type comparisons were performed using lacosamide spiking into different specimen types including serum, EDTA plasma, and heparin plasma. The correlation of results indicated that all specimen types were acceptable (r > 0.99). Stability studies showed that refrigerated extracted specimens were stable for 24 hours. Hemoglobin, triglycerides, and bilirubin did not significantly interfere with the measurement at lacosamide concentrations of 1.6 and 2 ìg/mL.
Conclusions & Discussion
A sensitive and robust LC-MS/MS method for lacosamide was developed and fully validated. The method demonstrates the potential for TDM of newer generation AEDs using LC-MS/MS. The rapid and simple procedure reported here is suitable for a high-throughput clinical laboratory.
References & Acknowledgements:
1. Krasowski M.D. Therapeutic drug monitoring of the newer anti-epilepsy medications. Matthew D. Krasowski. Pharmacoceuticals 2010, 3, 1909-1905.
2. Anderson G.D. Pharmacokinetic, pharmacodynamics, and pharmacogenetic targeted therapy of antiepileptic drugs. Therapeutic Drug Monitoring 2008, 30(2): 173-80.
3. Deeb S, McKeown D.A., Torrance H.J., Wylie F.M, Logan B.K., Scott K.S. Simultaneous analysis of 22 antiepileptic drugs in postmortem blood, serum and plasma using LC-MS-MS with a focus on their role in forensic cases.
IP Royalty: no
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