Pharmacokinetics of valacyclovir in the adult horse.

This study explores the pharmacokinetics of valacyclovir, a drug used to treat herpes virus type-1 infections in horses. Six adult horses were tested with different doses of the drug, and the researchers concluded that the ideal dosage to maintain effective serum acyclovir concentrations would be a loading dose of 27 mg/kg every 8 hours for 2 days, followed by a maintenance dose of 18 mg/kg every 12 hours.

About the Study

• The research was prompted by rising incidences of equine herpes virus type-1 infections. These infections have necessitated the development and proper dosage determination of an effective treatment protocol for horses.
• The study focused on the drug valacyclovir (VCV), a prodrug of acyclovir (ACV). A prodrug is a medication that, after administration, is metabolized into a pharmacologically active drug. In this case, VCV is converted into ACV in the body.

Research Methodology

• Six adult horses were involved in the experiment which was designed as a randomized cross-over study. This design ensures that the same subjects are used in each treatment group, effectively controlling for any variability among different horses.
• The horses were given treatments composed of 10 mg/kg ACV infused intravenously, 5 g VCV delivered intragastrically (IG), and 15 g VCV also administered IG.
• Serum samples were taken at predetermined times to assess the concentration of acyclovir using high-performance liquid chromatography, a technique used to separate, identify, and quantify each component in a mixture.

Key Findings

• Results indicated a mean bioavailability (the fraction of the administered drug that reaches the systemic circulation) of ACV from oral VCV of 60% after 5 g of VCV and 48% after 15 g VCV.
• Mean observed maximum serum ACV concentrations (C(max)) were recorded at 1.45 +/- 0.38 microg/mL after 5 g VCV, and at 5.26 +/- 2.82 microg/mL after 15 g VCV treatment.
• There was no significant difference in the bioavailability of ACV between the different dose rates of VCV, indicating a flat dose-response relationship within the tested dosage range.
• Based on these findings, it was suggested a loading dose of 27 mg/kg VCV every 8 hours for 2 days, followed by a maintenance dose of 18 mg/kg every 12 hours can maintain effective serum ACV concentrations for the treatment of equine herpesvirus type-1 infections.