Dosage adjustment of anti-epileptic drugs by therapeutic drug monitoring (TDM) is very useful, especially for the first-generation anti-epileptic drugs (AEDs). Microsampling—the collection of small volumes of blood—is increasingly considered a valuable alternative to conventional venous sampling for TDM. Volumetric absorptive microsampling (VAMS) allows accurate and precise collection of a fixed volume of blood, eliminating the volumetric blood hematocrit bias coupled to conventional dried blood spot collection. The aim of this study was to develop and validate an LC-MS/MS method for the determination and quantification of four anti-epileptic drugs (carbamazepine, valproic acid, phenobarbital, and phenytoin) and one active metabolite (carbamazepine-10,11-epoxide) in samples collected by VAMS. The method was fully validated based on international guidelines. Precision (%RSD) was below 10%, while, with a single exception, accuracy (%bias) met the acceptance criteria. Neither carry-over nor unacceptable interferences were observed, the method being able to distinguish between the isomers oxcarbazepine and carbamazepine-10,11-epoxide. All compounds were stable in VAMS samples for at least 1 month when stored at room temperature, 4 °C, and − 20 °C and for at least 1 week when stored at 60 °C. Internal standard-corrected matrix effects were below 10%, with %RSDs below 4%. High (> 85%) recovery values were obtained and the effect of the hematocrit on the recovery was overall limited. Successful application on external quality control materials and on left-over patient samples demonstrated the validity and applicability of the developed procedure.
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The authors wish to acknowledge Prof. Veronique Stove, PharmD. Matthijs Oyaert and their team for assistance with blood collection and all volunteers who participated in the study. Furthermore, SV would also like to thank the Special Research Fund (BOF) for granting her a PhD fellowship (application number 01D42414).
Approval for this study was provided by the Ethics Committee of Ghent University Hospital (EC2017/0572). For the use of left-over samples to evaluate an alternative procedure for AED monitoring, the need to obtained individual informed consent was waived by the Ethics Committee.
Conflict of interest
The author declares to not have any financial, commercial, legal, or professional relationship with other organizations, or with the people working with them, that could influence the matter discussed in this manuscript.
The original version of this article was revised: the headings of figure 2 of both graphs are the same.
A correction to this article is available online at https://doi.org/10.1007/s00216-018-0951-8.
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Velghe, S., Stove, C.P. Volumetric absorptive microsampling as an alternative tool for therapeutic drug monitoring of first-generation anti-epileptic drugs. Anal Bioanal Chem 410, 2331–2341 (2018). https://doi.org/10.1007/s00216-018-0866-4
- Anti-epileptic drugs
- Volumetric absorptive microsampling
- Liquid chromatography-tandem mass spectrometry
- Sample preparation
- Alternative sampling strategies