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Doctoral thesis, 2017

Dexamethasone in horses

Ekstrand, Carl


Equine athletes and companion horses are commonly treated with glucocorticoids such as dexamethasone. Care of sick or injured animals is vital for the animal welfare. To protect the integrity of equine sport, legal therapeutic substances are regulated during competition. The overall aim of this thesis was to provide quantitative information of dexamethasone exposure and response in Standardbreds and to relate this information to medication and anti-doping methodology. Dexamethasone-21-isonicotinate suspension administered intramuscularly and dexamethasone sodium phosphate solution administered both intravenously and intra- articularly were used in experiments. Dexamethasone was quantified in plasma, urine and synovial fluid by means of UHPLC-MS/MS. Cortisol response, IL-1β response, joint circumference response, local skin temperature response and lameness response were used as biomarkers. Dexamethasone plasma- and synovial fluid concentration-time courses were characterised by means of compartment modelling. The response-time courses were described by fitting a turnover model with an inhibitory function to experimental biomarker response data. Dexamethasone exposure was described in plasma and synovial fluid. In the Standardbreds studied, median dexamethasone plasma clearance was 0.51 L∙h-1∙kg-1 and median volume of distribution (at steady state) was 1.58 L∙kg-1. The median half-life in plasma and synovial fluid was 2.4 h and 1.3 h, respectively. After intramuscular administration of dexamethasone-21-isonicotinate, mean terminal half-life was 39 h due to slow release into plasma from the injection site. The dexamethasone concentration was 4- to 15-fold higher in urine than in plasma. A circadian cortisol baseline was described using a cosine function and cortisol response was characterised. Median potency value and for cortisol response in plasma was 0.039 ng∙mL-1 and the efficacy value was 0.92. Dexamethasone inhibited lameness and synovial fluid IL-1β release at doses lower than the approved. The median calculated synovial fluid concentration that suppressed lameness response by 50 % was 17 ng∙mL-1. The tentative potency value for IL-1β response was 19 ng∙mL-1. The information provided in this thesis can be used to improve future medication protocols and anti-doping controls which could improve animal welfare.


pharmacokinetics; pharmacodynamics; potency; efficacy; turnover model; integrative pharmacology; quantitative pharmacology; corticosteroids; glucocorticoids

Published in

Acta Universitatis Agriculturae Sueciae
2017, number: 2017:31
ISBN: 978-91-576-8835-4, eISBN: 978-91-576-8836-1
Publisher: Department of Biomedical Sicences and Veterinary Public Health, Swedish University of Agricultural Sciences

Authors' information

UKÄ Subject classification

Pharmacology and Toxicology

URI (permanent link to this page)