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Interlaboratory Variability in the Quantification of New Generation Antiepileptic Drugs Based on External Quality Assessment Data

Interlaboratory Variability in the Quantification of New Generation Antiepileptic Drugs Based on External Quality Assessment Data

John Williams, Meir Bialer, Svein I Johannessen, Günther Krämer, René Levy, Richard H Mattson, Emilio Perucca, Philip N Patsalos, John F Wilson

Epilepsia. 2003 Jan;44(1):40-5.

PMID: 12581228

Abstract:

Purpose:
To assess interlaboratory variability in the determination of serum levels of new antiepileptic drugs (AEDs).
Methods:
Lyophilised serum samples containing clinically relevant concentrations of felbamate (FBM), gabapentin (GBP), lamotrigine (LTG), the monohydroxy derivative of oxcarbazepine (OCBZ; MHD), tiagabine (TGB), topiramate (TPM), and vigabatrin (VGB) were distributed monthly among 70 laboratories participating in the international Heathcontrol External Quality Assessment Scheme (EQAS). Assay results returned over a 15-month period were evaluated for precision and accuracy.
Results:
The most frequently measured compound was LTG (65), followed by MHD (39), GBP (19), TPM (18), VGB (15), FBM (16), and TGB (8). High-performance liquid chromatography was the most commonly used assay technique for all drugs except for TPM, for which two thirds of laboratories used a commercial immunoassay. For all assay methods combined, precision was <11% for MHD, FBM, TPM, and LTG, close to 15% for GBP and VGB, and as high as 54% for TGB (p < 0.001). Mean accuracy values were <10% for all drugs other than TGB, for which measured values were on average 13.9% higher than spiked values, with a high variability around the mean (45%). No differences in precision and accuracy were found between methods, except for TPM, for which gas chromatography showed poorer accuracy compared with immunoassay and gas chromatography-mass spectrometry.
Conclusions:
With the notable exception of TGB, interlaboratory variability in the determination of new AEDs was comparable to that reported with older-generation agents. Poor assay performance is related more to individual operators than to the intrinsic characteristics of the method applied. Participation in an EQAS scheme is recommended to ensure adequate control of assay variability in therapeutic drug monitoring.

Chemicals Related in the Paper:

Catalog Number	Product Name	CAS Number	Price
AP145821609	Tiagabine Related Compound A	145821-60-9	Price
AP25451530	Felbamate Related Compound A	25451-53-0	Price
AP7529160	Vigabatrin Related Compound A	7529-16-0	Price

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