Abstract
Dexamethasone, formulated as sodium phosphate and as phenylpropionate combined with sodium phosphate, was administered subcutaneously to six greyhounds. Plasma and urine were collected for up to 240h and analysed with a limit of quantification (LOQ) of at least 100pg/ml for dexamethasone. Dexamethasone, formulated as sodium phosphate, terminal half-life was 10.4h in plasma and approximately 16h in urine, and at 96h, plasma hydrocortisone concentrations returned to background with dexamethasone levels around the LOQ. Dexamethasone, formulated as phenylpropionate combined with sodium phosphate, terminal half-life, was 25.6h in plasma and approximately 26h in urine, and at 96h, plasma hydrocortisone concentrations returned to background with dexamethasone levels in three of the six greyhounds around the LOQ. Critical assessment of the pharmacokinetic and pharmacodynamic data indicated how it might be utilized for medication control in racing greyhounds.
Highlights
Dexamethasone, a synthetic corticosteroid, is a commonly used veterinary medicine
Dexamethasone in plasma was measured for 10 h after administration, and the limit of quantification (LOQ) was 2 ng/ml. 1 mg of an undefined formulation of dexamethasone was injected intramuscularly into 25 greyhounds, and urine samples collected for up to 96 h (Hill et al, 1997) with dexamethasone being detected for 24 h
Note: Cmax, CL/F, HL. aHarmonic mean
Summary
Dexamethasone, a synthetic corticosteroid, is a commonly used veterinary medicine. Dexamethasone sodium phosphate is resorbed rapidly from the injection site, ensuring a rapid onset of activity, whereas dexamethasone phenylpropionate is absorbed more slowly from the injection site, ensuring a more prolonged duration of activity (Australian Pesticides & Veterinary Medicines Authority, 2002). There are limited data on the pharmacokinetics of dexamethasone in dogs. 1 mg of an undefined formulation of dexamethasone was injected intramuscularly into 25 greyhounds, and urine samples collected for up to 96 h (Hill et al, 1997) with dexamethasone being detected for 24 h. For medication control of drugs for animals used in sport, urine is the sample matrix of choice (Morris, 2014). To inform risk assessment for medication control, information on contemporaneous plasma (as plasma levels drive effects) and urine levels, after clinical
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