Systemic detectability of dexamethasone and prednisolone after eye drop application in horses.
Authors: Stucki Michael, Voegel Clarissa D, Binz Tina M, Kraemer Thomas, Lavaud Arnold, Voelter Katrin
Journal: Equine veterinary journal
Summary
# Systemic Detectability of Dexamethasone and Prednisolone After Eye Drop Application in Horses Topical corticosteroid eye drops are routine therapeutic agents in equine practice, yet sport governing bodies classify systemic steroids as prohibited substances—creating potential compliance uncertainty when treating competing horses. This prospective cohort study examined whether dexamethasone (Maxitrol® 0.1%) and prednisolone (Pred Forte® 1%) eye drops, administered three times daily for 14 days to 11 horses (5 and 6 eyes respectively), would produce detectable systemic concentrations using liquid chromatography-tandem mass spectrometry. Both drugs achieved measurable serum and urine levels throughout treatment, with dexamethasone concentrations ranging 0.7–43 ng/mL (serum) and 1.2–5 ng/mL (urine), whilst prednisolone proved more systemically available at 1.1–32.5 ng/mL and 3.7–19 ng/mL respectively. Critically, dexamethasone fell below the limit of detection within 24 hours of cessation, whereas prednisolone required approximately one week for urine clearance and up to three weeks for complete serum clearance. For practitioners advising competition horses, these findings underscore the necessity of withdrawing topical corticosteroid treatment sufficiently in advance of doping controls—particularly prednisolone, which demonstrates longer systemic retention and greater urinary excretion.
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Practical Takeaways
- •Ophthalmologists and general practitioners must counsel horse owners that standard corticosteroid eye drop treatment will trigger positive doping tests during the 14-day treatment period and for variable periods afterward (up to 7 days post-treatment)
- •Competing horses requiring topical corticosteroid therapy for eye conditions should plan treatment timing to allow adequate clearance periods: minimum 1 day for dexamethasone, minimum 7 days for prednisolone after treatment cessation
- •This finding has significant implications for sport horse welfare—practitioners should advocate for clearer guidelines distinguishing therapeutic ophthalmic use from performance-enhancing systemic doping
Key Findings
- •Dexamethasone eye drops (0.1%, 3× daily for 14 days) produced detectable serum levels (0.7-43 ng/mL) and urine levels (1.2-5 ng/mL) throughout treatment
- •Prednisolone eye drops (1%, 3× daily for 14 days) produced detectable serum levels (1.1-32.5 ng/mL) and urine levels (3.7-19 ng/mL) throughout treatment
- •Dexamethasone became undetectable 24 hours after treatment cessation; prednisolone became undetectable in urine by day 15 and serum by day 21
- •Both topical corticosteroids can generate positive doping results in equine sport competition samples during and immediately after treatment