title: Pharmacokinetics of valacyclovir in the adult horse.
abstract: Recent outbreaks of equine herpes virus type-1 infections have stimulated renewed interest in the use of effective antiherpetic drugs in horses. The purpose of this study was to investigate the pharmacokinetics of valacyclovir (VCV), the prodrug of acyclovir (ACV), in horses. Six adult horses were used in a randomized cross-over design. Treatments consisted of 10 mg/kg ACV infused intravenously, 5 g (7.7-11.7 mg/kg) VCV delivered intragastrically (IG) and 15 g (22.7-34.1 mg/kg) VCV administered IG. Serum samples were obtained at predetermined times for acyclovir assay using high-performance liquid chromatography. Following the administration of 5 g VCV, the mean observed maximum serum ACV concentration (C(max)) was 1.45 +/- 0.38 (SD) microg/mL, at 0.74 +/- 0.43 h. At a dose of 15 g VCV, the mean C(max) was 5.26 +/- 2.82 microg/mL, at 1 +/- 0.27 h. The mean bioavailability of ACV from oral VCV was 60 +/- 12% after 5 g of VCV and 48 +/- 12% after 15 g VCV, and did not differ significantly between dose rates (P > 0.05). Superposition suggested that a loading dose of 27 mg/kg VCV every 8 h for 2 days, followed by a maintenance dose of 18 mg/kg every 12 h, will maintain effective serum ACV concentrations.
authors.affiliation: Department of Physiological Sciences, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK 74078, USA. lk.maxwell@okstate.edu
authors.forename: L K
authors.initials: LK
authors.lastname: Maxwell
authors.forename: B G
authors.initials: BG
authors.lastname: Bentz
authors.forename: D W A
authors.initials: DW
authors.lastname: Bourne
authors.forename: R S
authors.initials: RS
authors.lastname: Erkert
mesh_terms: D000212:Acyclovir / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood / Q000493:pharmacokinetics; D000284:Administration, Oral; D000818:Animals; D000998:Antiviral Agents / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D019540:Area Under Curve; D001682:Biological Availability; D002851:Chromatography, High Pressure Liquid; D005260:Female; D006207:Half-Life; D006736:Horses; D007262:Infusions, Intravenous; D008297:Male; D008657:Metabolic Clearance Rate; D000077483:Valacyclovir; D014633:Valine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood / Q000493:pharmacokinetics
chemical_list: D000998:Antiviral Agents; D014633:Valine; D000077483:Valacyclovir; D000212:Acyclovir