Serum and synovial fluid steady-state concentrations of trimethoprim and sulfadiazine in horses with experimentally induced infectious arthritis.

The research article investigates the effect of various dosages of the combined drugs trimethoprim and sulfadiazine on horses with experiments-induced infectious arthritis. It concludes that a higher twice-daily dosage of the medicine was effective in maintaining therapeutic chemical concentrations in the blood and fluid of the infected joint.

Research Context

• The research seeks to evaluate the efficacy of the antibiotics trimethoprim (TMP) and sulfadiazine (SDZ) in treating infectious arthritis in horses.
• The study focuses particularly on the concentrations of TMP and SDZ in the blood (serum) and joint fluid (synovial fluid) of horses inflicted with arthritis.

Methodology

• The tarsocrural joints (a joint in the hock of the horse) of eleven horses were infected with Staphylococcus aureus bacteria, which were proven susceptible to the TMP-SDZ combination with a certain minimum inhibitory concentration (MIC).
• The MIC, the lowest concentration of the drug that prevents bacterial growth, was determined to be 0.25 micrograms/ml of TMP and 4.75 micrograms/ml of SDZ.
• The researchers administrated the TMP-SDZ combination orally in two different dosages: 30 mg/kg body weight once daily, and 60 mg/kg divided into two doses of 30 mg/kg every 12 hours.
• Samples of blood and joint fluid were taken before infection, after infection but before the treatment, and at different times after the treatment has begun.
• The samples were taken three days after continuous drug administration, at which point a steady-state concentration of the drugs in the body would have been reached.

Results and Conclusion

• The lower dosage of the TMP-SDZ combination (30 mg/kg once daily) was concluded to be ineffective as it failed to maintain TMP or SDZ concentrations above the MIC in the infected joint fluid or the blood serum.
• The higher dosage (60 mg/kg given as two doses of 30 mg/kg) proved effective in maintaining drug concentrations in the serum and joint fluid above the MIC for the infective bacteria.
• The study concludes that the higher dosage, administered twice a day, could be the more effective regimen to sustain therapeutic drug concentrations in both serum and synovial fluid for horses suffering from bacterial arthritis.