Regulatory significance of procaine residues in plasma and urine samples: preliminary communication.

This research studied the presence and effects of procaine, a local anaesthetic, in horses. Specifically, the investigation focused on the concentration of procaine in horse plasma and urine, the duration of its effects, and the significant alteration of effects when combined with epinephrine.

Study on Plasma and Urinary Concentrations of Procaine

• The experiment scrutinized the levels of procaine, a local anaesthetic, found in horses’ plasma and urine after it was administered.
• Initially, a clinical dose of 80mg procaine was used, but the resulting concentration in plasma was below the lower quantification limit, rendering it unsuitable to set a threshold.
• Subsequently, the concentration of procaine was measured in the horses’ urine. This was done using a dose of 5mg procaine, representing the highest dose that showed no effect (HNED) on horses.

Threshold Findings for Procaine in Horses’ Urine

• The research identified the peak concentration of free unconjugated procaine in equine urine as 23.7 ng/mL. The highest level of total procaine, comprising both unconjugated and conjugated, was 37.9 ng/mL.
• Given that basic drugs like procaine can accumulate greatly in acidic urine, the study proposed a reasonable and conservative threshold concentration of 25 ng/mL of unconjugated procaine.

Study on the Effects of Procaine and Epinephrine in Horses

• Horses were administered various doses of procaine for local anaesthetic experiments. The horses were also given doses of 2% procaine with added epinephrine.
• Even without epinephrine, all doses of procaine produced a local anaesthetic effect with durations that varied depending on the dose. However, when epinephrine was added, the duration of the anaesthetic effect significantly increased.
• The longest effects without epinephrine lasted for 60 minutes (320mg dose), while the effects after adding epinephrine could extend up to 420 minutes (320mg dose).

Regulatory Implications

• The research highlights regulatory implications as the addition of epinephrine to procaine increases the duration of the local anaesthesia. This extension could surpass a reasonable confinement period for horses before a race, which could potentially lead to unfair sporting outcomes or animal welfare issues.