Poster Presentation 24th International Conference of Racing Analysts and Veterinarians 2026

Establishing Residue Limits for Procaine in Greyhound Racing: Addressing Feed-Related Positives through Pharmacokinetic Modelling (130446)

Steven Karamatic 1 , Paul Zahra 2 3 , Tim Morris 4 5 , Stuart Paine 5
  1. Greyhound Racing Victoria, West Melbourne, Victoria, Australia
  2. Racing Analytical Services Ltd, Flemington, VIC, Australia
  3. Currently at Shimadzu Australasia, Belmont, Western Australia, Australia
  4. Greyhound Board of Great Britain, London, United Kingdom
  5. School of Veterinary Medicine and Science, University of Nottingham, Leicestershire, United Kingdom

Procaine, a short-acting local anaesthetic, more commonly co-formulated with penicillin to extend its duration of action, presents a regulatory challenge in greyhound racing due to its presence in knackery meat. Despite no recent administration to the greyhound, procaine has frequently been detected in racing samples assumed to follow ingestion of contaminated meat derived from livestock treated with procaine penicillin prior to slaughter. Some jurisdictions historically adopted a pragmatic ‘threshold’ of 1,000 ng/mL in urine; this paper proposes more suitable residue limits for plasma and urine following an administration study, pharmacokinetic analysis, and risk analysis.

Six greyhounds were intramuscularly administered 4 mL of Benacillin® (containing 150 mg/mL procaine penicillin and 20 mg/mL procaine hydrochloride) – equivalent to ~10 mg/kg procaine. Plasma and urine samples were collected over 14 days.

Plasma (0.5 mL) or hydrolysed urine (1 mL) was subject to solid phase extraction (SPE) then analysed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) with procaine-d10 as internal standard for quantification. The limit of quantification was estimated to be 0.25 ng/mL in plasma and 1.0 ng/mL in urine from validation that also assessed specificity, accuracy, precision, recovery and matrix effects.

Peak urine concentrations exceeded 200,000 ng/mL between 4–8 hours post-dose, before declining and entering a terminal phase between 50–100 hours (similar to plasma), declining below 200 ng/mL by 48–72 hours. Plasma concentrations fell below 5 ng/mL by 72 hours. A three-compartment dual absorption pharmacokinetic model was developed. Extrapolating from equine research, ≤5ng/mL in plasma was used to represent a marker of an irrelevant pharmacological effect at a local site. Using Toutain approach, residue limits of 200 ng/mL (urine) and 5 ng/mL (plasma) were introduced, with detection time of 120 hours. An adverse analytical finding is unlikely if knackery meat contaminated with ≤3mg/kg of procaine (30x Australian MRL) is withheld for 24–48 hours pre-race.