Pharmacokinetics of a FDA-labeled dose of diclazuril administered orally once weekly to adult horses.

This study explores the effects of administering a regular FDA-approved dose of diclazuril, a prophylactic drug, to adult horses, with the aim of finding steady-state concentrations that can hinder the growth of Sarcocystis neurona, a parasite causing Equine protozoal myeloencephalitis (EPM), a debilitating neurological disease in horses.

Objective and Methodology

• The research aimed to determine the efficacy and reliability of using the FDA-approved dosage (1mg/kg of 1.56% diclazuril, also known as Protazil) on a weekly basis. The objective was to achieve steady plasma concentrations of the drug that could consistently inhibit S. neurona in healthy adults horses.
• Eight adult horses were administered five separate weekly doses of the drug. Before and 10 hours after each drug administration, blood samples were taken via venipuncture. After the last (fifth) dose, additional blood samples were taken every 24 hours for a week.
• The plasma samples obtained through this process were analyzed using high-pressure liquid chromatography, and the pharmacokinetic analysis was completed through a nonlinear mixed effects model.

Findings and Conclusion

• The results indicated that the averages of the peak plasma concentration of the drug were 264 ng/mL and the terminal half-life was 3.6 days.
• The important conclusion derived from this study is that the weekly oral dose of FDA-approved diclazuril in healthy horses is able to maintain steady plasma drug concentrations. These concentrations are known to inhibit growth of S. neurona in lab conditions.
• Therefore, on the basis of the study’s findings, it can potentially be assumed that the prescribed dosage strategy is effective in offering prophylactic protection against EPM in horses.

Implication of the Study

• This research is particularly significant as it is geared towards fighting Equine protozoal myeloencephalitis, a major neurological disease commonly found in horses in America, especially the younger, performance-focused ones.
• The study provides evidence and confidence in the preventive medication strategies for EPM by establishing the efficacy and regular dosing requirements of diclazuril for adult horses.
• Such findings can help in better management of EPM, by providing an effective prophylactic treatment strategy.