Prednisolone, a corticosteroid frequently used in veterinary medicine with anti-inflammatory, analgesic and immunosuppressive properties, is most used in racing greyhounds as topical eye drops for ongoing management of chronic superficial keratitis (pannus). Treatment is essential for welfare, but corticosteroids affect energy metabolism, potentially increasing fatigue threshold, so systemic concentrations may confer performance-enhancing effects. Additionally, as in equine, there are concerns that prednisolone may be naturally present in canine urine samples, requiring a urinary threshold rather than a screening limit. This study aimed to characterise the pharmacokinetics of prednisolone in greyhounds, inform risk management, harmonise reporting criteria for racing chemists, and guide veterinarians in determining appropriate withdrawal times.
Six greyhounds were administered 1 mg/kg of prednisolone orally. Plasma and urine samples were collected over five days. Results are compared with an earlier topical ocular dosing study that administered Prednefrin Forte® (Prednisolone acetate 10 mg/mL) one drop/eye to eight greyhounds for five days. Urine samples were collected for two days after last treatment.
Plasma (0.5 mL) or urine (1 mL) was subject to solid phase extraction (SPE) then analysed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) with prednisolone-d8 as internal standard for quantification. The limit of quantification was estimated to be 0.1 ng/mL in plasma and urine from validation that also assessed specificity, accuracy, precision, recovery and matrix effects.
Pharmacokinetic analysis was completed and is presented. Oral dosing produced peak urinary concentrations exceeding 11,000 ng/mL at 2–4 hours, reducing to < 3 ng/mL by 48 hours, and most not detectable by 96–120 hours. Ocular dosing resulted in peak concentrations below 200 ng/mL, < 10 ng/mL by 20 hours, and most not detectable within 24–32 hours.
Interpretation and resultant medication control is complicated by other sources of prednisolone that will be discussed. A 50 ng/mL threshold in urine was introduced.