Pharmacokinetics of methylprednisolone acetate after intra-articular administration and subsequent suppression of endogenous hydrocortisone secretion in exercising horses.

The research is aimed at studying the pharmacokinetics of methylprednisolone (MP), its relationship with hydrocortisone (HYD), and their presence in the plasma and urine of horses after intra-articular administration. The study also attempts to understand how these findings might aid in identifying use of glucocorticoids in horses and help in their treatment.

Methodology

• The study was conducted on five Thoroughbred mares of three years old.
• The horses were made to exercise on a treadmill thrice a week during the study period.
• Initially, the horses were given 100 mg of methylprednisolone acetate (MPA) intra-articularly. Eight weeks later, they received a larger dose of 200 mg of MPA in the same manner.
• Following administration of each dose of MPA, plasma and urine samples were collected at various points for eight weeks. These samples were examined to determine the concentrations of MP and HYD.
• Compartmental and non-compartmental pharmacokinetic-pharmacodynamic parameters were then established based on these concentrations.

Results

• The maximum concentration of MP in plasma was found to be similar for both MPA doses. These concentrations stayed significantly higher than the lower limit of quantitation for 18 days post administration of 200 mg of MPA, and for 7 days following 100 mg of MPA administration.
• Both the maximum concentration and the area under the observed concentration-time curve for MP in urine were about 10 times and 17 times higher respectively, after the 200 mg MPA dose compared to the 100 mg dose.
• After administration of both MPA doses, the HYD concentration in the plasma and urine of all the horses dropped below quantifiable limits for at least 48 hours.

Conclusion

• The research concludes that the pharmacokinetics of MP may vary based on different intra-articular MPA dosing regimes, and that MP may be detected in plasma and urine for a longer duration than previously documented.
• This information may assist veterinarians in better treating sport horses. The study also suggests further research to determine whether assessing plasma HYD concentration can help in identifying those horses which have received exogenous glucocorticoids.