Pharmacokinetics of trimethoprim/sulphachlorpyridazine in horses after oral, nasogastric and intravenous administration.

This research paper explores the pharmacokinetic properties (how a drug is absorbed, distributed, metabolized, and excreted in the body) of a combined drug treatment of trimethoprim (TMP) and sulphachlorpyridazine (SCP) in horses. The study compares the results when the drugs are administered through different routes: orally (mixed with feed), nasogastrically (through a tube into the stomach), and intravenously (into the bloodstream).

Research Methodology

• The study involved eight adult horses monitored over a week.
• The horses were given a dosage of 5 mg/kg of TMP and 25 mg/kg of SCP, administered via various methods.
• The plasma concentrations of the drugs were measured over a period of 48 hours.
• Relevant pharmacokinetic parameters (distribution and elimination half-lives, clearance rate, bioavailability, and volume of distribution) were determined for both TMP and SCP.

Results

• After intravenous administration, the volume of distribution at steady-state (Vd(ss)) was significantly larger for TMP than for SCP.
• The clearance rates were 7.73 +/- 2.26 mL/min.kg for TMP and 2.64 +/- 0.48 mL/min.kg for SCP.
• Peak plasma concentrations (Cmax) and the bioavailabilities (F) of both drugs were significantly reduced when mixed with feed (concentrate) compared to nasogastric administration.
• Plasma concentration-time curves after feed administration displayed a biphasic absorption pattern, with the first peak happening 1-2 hours after administration, and the second peak 8-10 hours later.

Conclusion

Based on the research conducted, the administered method significantly impacts the pharmacokinetic properties of TMP and SCP in horses. In particular, the drug combination’s bioavailability was reduced when the drugs were mixed with concentrate compared to administering them via a nasogastric tube. This work has broad implications for how TMP and SCP – and potentially other drugs – are administered in veterinary medicine for maximized effect.