|Acyclovir was administered IV (10 mg/kg in 1 L isotonic crystalloid solution over 60 minutes) and orally (20 mg/kg) to healthy adult horses.
Plasma samples were obtained and acyclovir concentrations were determined by high-pressure liquid chromatography.
Peak concentration (meanÂ±SD) for IV acyclovir was 13.74Â±5.88 g/mL at the completion of the 1-hour infusion.
The half-life of the distribution phase () was 0.16 hours while the half-life of the elimination phase () was 9.6 hours.
The steady-state volume of distribution was 3.93Â±1.21 L/kg.
We were unable to measure pharmacokinetics after PO acyclovir as plasma concentrations were below the lower limits of detection in all 6 horses.
Conclusions: IV administration of acyclovir to healthy adult horses achieves concentrations within the sensitivity range described for equine herpes virus-type 1.
The oral bioavailability of acyclovir in horses is low and additional studies are required.
Source: Wilkins, Pamela A., Papich, Mark & Sweeney, Raymond W. (2005): Pharmacokinetics of acyclovir in adult horses. In: Journal of Veterinary Emergency and Critical Care 15 (3), 174-178.
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