Pharmacokinetics and metabolism of dantrolene in horses.

The research paper studies the metabolic process and pharmacokinetics of dantrolene, a muscle relaxant used in performance horses, investigating its formulation in capsule or paste form and its metabolism in the horse’s body.

Objective and Design of the Study

• The research aims to better understand cytochrome P450-mediated metabolism of dantrolene in horses and explore the pharmacokinetics of the drug in two different formulations – capsule and paste.
• The study adopts a randomized, balanced 2-way crossover design wherein eight healthy horses were administered one of two formulas of the drug, followed by a four-week washout period before receiving the other variant.

Methodology and Data Analysis

• Horses received a single oral dose of either capsules or paste at the start followed by the other formulation after the washout period.
• Blood samples were taken prior to drug administration and at various times up to 96 hours after administration.
• The plasma samples were examined using liquid chromatography-mass spectrometry and the data produced was analyzed through both noncompartmental and compartmental analysis methods.

Findings and Conclusion

• Finding has shown that dantrolene metabolizes quickly to 5-hydroxydantrolene in vivo and in vitro, indicating that two distinct enzymes might be responsible for the drug’s metabolism.
• The plasma concentrations for capsules and paste peaked at 28.9 ± 21.6 and 37.8 ± 12.8 ng/mL respectively, occurring at approximately 3.8 hours for both preparations.
• Dantrolene and 5-hydroxydantrolene, its major metabolite, both fell below the detection limit in plasma and urine by 168 hours after administration.
• In conclusion, this study provides valuable insights into the pharmacokinetics and metabolism of dantrolene in horses, aiding in optimizing the dosing and administration schedules for this important skeletal muscle relaxant.