[Demonstration of two trimethoprim/sulfonamide combinations in bronchoalveolar lavage fluid of horses and determination of blood levels].

This research project investigated the concentration and persistence of two different combinations of trimethoprim/sulfonamide drugs in the bronchoalveolar lavage fluid and blood of horses. The researchers used healthy horses, varying dosages methods, and took samples at various intervals to detect levels of the drugs and their elimination half-lives.

Methods and Medication Administration

• The study utilized five healthy horses, in which two different combinations of trimethoprim/sulfonamide drugs were administered – a sulfadoxine/trimethoprim combination was given intravenously (IV) on the first day, while a sulfadimethoxine/trimethoprim combination was administered orally once daily for ten days.
• A control horse was used for comparison, which was not given any medication.
• The researchers performed six bronchoalveolar lavages on each horse. Bronchoalveolar lavage is a procedure where a bronchoscope is passed into the lungs and a fluid sample is collected for examination.

Drug Level Measurement and Findings

• Blood samples were collected to gauge blood levels and calculate the drugs’ elimination half-lives, which is the time it takes for the concentration of the drug to reduce by half in the bloodstream.
• The high-performance liquid chromatography (HPLC) technique was used to measure the quantity of the drugs in the lavage fluid and plasma. HPLC enables efficient separation and quantification of the components in a mixture, in this case, the drug substances.
• Findings showed low amounts of sulfonamides and trimethoprim in lavage fluid samples. These drugs seemed to concentrate more in the bloodstream than in the lung fluids.

Results and Conclusion

• Thirty minutes following the IV administration, the average plasma concentration of sulfadoxine and trimethoprim was 71.6 and 1.13 micrograms/g respectively, while 24 hours later, the sulfadoxine level significantly dropped to 3.0 micrograms/g, and trimethoprim became undetectable.
• The documented average elimination half-lives of sulfadoxine and trimethoprim were 7.94 hours and 1.35 hours, respectively.
• Eight hours after oral application, the highest mean sulfadimethoxine blood levels of 53.8 micrograms/g were measured and the elimination half-life of this drug was noted as 9.77 hours. The maximum mean trimethoprim concentration of 0.32 microgram/g plasma appeared in blood samples taken two hours after drug administration.

This research provides valuable information about these drug combinations in the treatment of equine respiratory diseases, particularly in terms of their concentration and duration of effectiveness within the horse’s system. The negligible levels in bronchoalveolar fluid suggest that these drugs may not be highly effective for lung infections. Further research is needed to investigate alternative treatment options.