Variability in plasma concentrations of methylprednisolone 6 days after intrasynovial injection of methylprednisolone acetate in racing horses: A field study.

The study examines the variability in blood concentrations of a drug called methylprednisolone (MP) in racehorses when used with hyaluronic acid (HA) and on different joints of the horse. The goal of the research was to study whether the characteristics of the injection such as the joint it was injected into, and whether it was used in combination with HA, influenced the length of time that the drug remained in the horse’s system.

Methodology

• The researchers carried out a field study with 76 actively racing horses, spanning different disciplines: Thoroughbred, Standardbred and Quarter Horse racing.
• These horses each received an injection of 100 mg of methylprednisolone acetate, a steroid used to manage inflammation in synovial structures (the fluid-filled areas of a joint), which is a common occurrence in horse racing.
• To examine the effects of the injection’s characteristics, they grouped the data based on the part of the horse’s joint the injection was given into and whether the injection was given in conjunction with hyaluronic acid (HA), a substance that complements the action of MP.
• Blood plasma was collected before the injection and 6 days after the injection to measure the concentrations of MP.

Results

• The mean concentration of MP in the plasma of all the horses after 6 days was found to be 96 ± 104 pg/mL.
• Where the MP was injected into the MCP joint, 86% of the data was censored, meaning these results were excluded from the statistical analysis.
• The team discovered that the concentration of MP in the plasma was lower when the injection was into the carpal joints as compared to when the injection was into the distal tarsal joints or medial femorotibial joints.
• The concentration of MP was also lower when the HA was not included in the injection, implying that HA may enhance or prolong the presence of MP in the horse’s system.

Conclusions

• Since the type of synovial structure injected varied by the racing discipline, the study could not determine any differences based on the racing discipline itself.
• The researchers concluded that practitioners should be aware that the use of MP acetate in conjunction with HA, as well as its use on distal tarsal joints or medial femorotibial joints, might prolong the time it remains in the horse’s system. This is an important consideration for managing withdrawal times before competitions in regulated equine sports, as it helps prevent illicit drug use.