Pharmacokinetics of guaifenesin following administration of multiple doses to exercised Thoroughbred horses

H. K. Knych, S. D. Stanley, D. Benson, R. M. Arthur

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Guaifenesin is an expectorant commonly used in performance horses to aid in the clearance of mucus from the airways. Guaifenesin is also a centrally acting skeletal muscle relaxant and as such is a prohibited drug with withdrawal necessary prior to competition. To the authors' knowledge, there are no reports in the literature describing single or multiple oral administrations of guaifenesin in the horse to determine a regulatory threshold and related withdrawal time. Therefore, the objective of the current study was to describe the pharmacokinetics of guaifenesin following oral administration in order to provide data upon which appropriate regulatory recommendations can be established. Nine exercised Thoroughbred horses were administered 2 g of guaifenesin orally BID for a total of five doses. Blood samples were collected immediately prior to drug administration and at various times postadministration. Serum guaifenesin concentrations were determined and pharmacokinetic parameters calculated. Guaifenesin was rapidly absorbed (Tmax of 15 min) following oral administration. The Cmax was 681.3 ± 323.8 ng/mL and 1080 ± 732.8 following the first and last dose, respectively. The serum elimination half-life was 2.62 ± 1.24 h. Average serum guaifenesin concentrations remained above the LOQ of the assay (0.5 ng/mL) by 48 h postadministration of the final dose in 3 of 9 horses.

Original languageEnglish
Pages (from-to)416-419
Number of pages4
JournalJournal of Veterinary Pharmacology and Therapeutics
Issue number4
StatePublished - Aug 1 2016

Bibliographical note

Publisher Copyright:
© 2016 John Wiley & Sons Ltd

ASJC Scopus subject areas

  • Pharmacology
  • General Veterinary


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