|Pharmacokinetics of acyclovir in adult healthy horses
Acyclovir is an antiviral drug which is commonly used in human medicine, especially in treating herpes labialis infections. Sometimes it is also used in horses but less is known about its pharmakokinetics. An interesting study - who knew that the substance does not reach therapeutical levels after oral adminisration?|
|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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