Pharmacokinetics of methylprednisolone acetate after intra-articular administration and its effect on endogenous hydrocortisone and cortisone secretion in horses.

The research investigated how methylprednisolone acetate, injected directly into the joint of a horse, affected the levels of the horse’s naturally occurring steroids, hydrocortisone and cortisone. The study found that this treatment significantly reduced hydrocortisone and cortisone levels for as long as 240 hours after the injection.

Research Methods

The research methods consisted of several steps:

• Six thoroughbred horses participated in the study.
• Each horse received an intra-articular injection of 200 mg of methylprednisolone acetate (MPA) into a carpal joint. An intra-articular injection is an injection given directly into a joint.
• Scientists used liquid chromatography-mass spectrometry, a technique used to identify and quantify compounds in a sample, to determine the plasma concentrations of methylprednisolone (MP), hydrocortisone (HYD), and cortisone (COR) in the horses.

Research Findings

After performing these steps and analyzing the data, the researchers arrived at several findings:

• The transfer half-life of MP from the joint to the plasma was 1.7 hours, and the elimination half-life from plasma was 19.2 hours. Half-life refers to the time it takes for the quantity of a drug in the body to reduce by half.
• The maximum plasma concentration of MP was 7.26 +/- 3.3 ng/mL at 8 hours after the injection, which dropped to 0.11 +/- 0.08 ng/mL at 144 hours after the injection.
• Three hours after the MPA injection, the plasma concentrations of COR and HYD significantly decreased from their baseline values.
• The secretion of endogenous corticosteroids remained suppressed for as long as 240 hours after the injection.

Conclusion

The researchers concluded that intra-articular administration of MPA had a profound effect on HYD and COR secretion in horses, and that this effect lasted for up to 240 hours after the injection. This demonstrates the potential impact of this treatment on a horse’s naturally occurring steroids. The researchers also noted that the method used in the research was sensitive enough to fully describe the kinetics of MP, HYD, and COR after MPA administration.