Gabapentin in horses: Validation of an analytical method for gabapentin quantitation

A. F. Lehner, J. Stewart, A. Dafalla, K. J. Ely, A. L. Connerly, C. N. Jones, H. Elkholy, K. Thompson, T. Tobin, L. Dirikolu

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Gabapentin [1-(aminomethyl)cyclohexaneacetic acid, Neurontin®], is a new anticonvulsant used as adjunctive therapy in the treatment of partial seizures in humans not controlled with standard antiseizure drugs, and it has also been used in veterinary medicine. In performance horses, gabapentin is listed as a class 3 performance-enhancing substance by the Association of Racing Commissioners International, and thus is considered to have the potential to influence the outcome of races. Therefore, we developed and validated a sensitive gas chromatographic-mass spectrometric (GC-MS) method for gabapentin detection. Gamma-aminobutyric acid-d2 (GABA-d2) was used as an internal standard during solid-phase extraction; lacking the cyclohexyl ring of gabapentin, GABA-d2 formed a lactam structure to only a minor extent. Gabapentin, on the other hand, readily formed a lactam on thermal exposure during trimethylsilyl-derivatization and/or GC analysis; electrospray-ionization MS was employed to verify that the original compound was present as the expected 171 m.w. compound. Extraction efficiency for the assay was about 60%, and a curvilinear standard curve ranging from 50 ng/mL to 3000 ng/mL provided excellent within-run and between-run coefficients of variation and accuracies over a range of low, medium, and high values. The limit of detection, defined as the concentration calculated from the mean response at zero concentration plus two times the standard deviation, was calculated at 7.6 ng/mL; the limit of quantitation, defined as the concentration calculated from the mean of the zero responses plus five times the standard deviation, was calculated at 17 ng/mL. This method will enable accurate quantification of gabapentin in equine biological fluids for use in both pharmacokinetic and forensic studies.

Original languageEnglish
Pages (from-to)555-565
Number of pages11
JournalJournal of Analytical Toxicology
Issue number9
StatePublished - 2007

Bibliographical note

Funding Information:
This research was supported by grants from the Birmingham Racing Commission Breeding and Development Fund, Birmingham, AL, and Tuskegee University Research and Graduate Studies Development Fund, Tuskegee, AL. The authors thank Pharsight Corporation (Cary, NC) for providing WinNonlin, version 5.1, for pharmacokinetics analysis.

ASJC Scopus subject areas

  • General Medicine


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