Pharmacokinetic interactions between flunixin and sulphadimidine in horses.

This research studies the pharmacokinetic interactions between two drugs, flunixin and sulphadimidine, in horses. The study reveals that pre-medication with flunixin changes the way sulphadimidine behaves in the horse’s body, suggesting caution when using these drugs together.

Methodology

• The researchers studied how the body absorbs, distributes, metabolizes, and excretes sulphadimidine in both healthy horses and those pre-medicated with flunixin.
• Both intravenous and oral administration of 100 mg/kg body weight of sulphadimidine were used.
• The level of sulphadimidine in the horses’ bloodstream was measured using high-performance liquid chromatography (HPLC).

Findings

• After an intravenous injection of sulphadimidine, the researchers found that:
  • The rate at which sulphadimidine moved back to the central compartment from peripheral tissues increased by 67% in flunixin-medicated horses.
  • There was an apparent increase of 30% in K12, a term that indicates the rate of transfer of the drug to the peripheral compartments.
  • The half-life, or the time it takes for the amount of the drug in the horse’s body to reduce by half, decreased by 21%.
  • The volume of distribution at steady state (Vdss), an indication of how much the drug spreads throughout the body, decreased by 18%.
  • The mean residence time (MRT), or the average time the drug stays in the body, decreased by 20%.
• In the case of oral administration of sulphadimidine, the investigators noted that:
  • Sulphadimidine was quickly absorbed in both control and flunixin-medicated horses with half-lives of 0.5 and 0.43 hours, respectively.
  • The peak plasma concentration levels were 93.7 and 109 micrograms/ml, reached at 2.36 and 1.9 hours, respectively.
  • The half-life of the drug was shorter in flunixin pre-medicated horses than in control horses.
  • The systemic bioavailability of sulphadimidine, or the extent to which the drug successfully enters the body’s system, was 79.3% in control horses and 71.2% in flunixin medicated horses.

Conclusion

• The findings indicate that the use of flunixin significantly alters the pharmacokinetics of sulphadimidine.
• Given these interactions, the researchers recommend caution when administering sulphadimidine to horses that are also receiving flunixin.