Multiple oral dosing of valacyclovir in horses and ponies

Sequential Cerebrospinal Fluid Sampling in Horses: Comparison of Sampling Times and Two Different Collection Sites

Analysis of the cerebrospinal fluid (CSF) is important as a complementary test in horses with neurologic diseases, and sequential analysis may provide information about the treatment response or evolution and quantitative measures of the CSF drug concentration during treatment. The aim of this study was to compare erythrocyte and nucleated cell counts and protein concentration in multiple CSF samples obtained sequentially from two different puncture sites in clinically healthy horses. Eight and 12 horses, with no evidence of neurologic disease, were subjected to CSF collection from the atlanto-occipital (AO) and C1-C2 spaces, respectively. Cytologic and chemical analyses were performed on the CSF obtained at five sampling times (T1, T2, T3, T4, and T5). Repeated measures models were used to compare the mean erythrocyte count, nucleated cell count, and total protein concentration between the AO and C1-C2 groups at each sampling time. C1-C2 CSF had a significantly higher total protein concentration at T1 and T4 than that of AO CSF. All total protein concentration values remained within the reference interval (<90 mg/dL) for all sampling times and groups. No statistical difference was present between results at T2, T3, T4, and T5 and at T1 in both groups for all analyses. In conclusion, five consecutive AO or C1-C2 CSF collections with at least a 7-d interval did not result in alterations in the CSF erythrocyte and nucleated cell counts and total protein concentrations and did not interfere with the CSF analysis results.

Antiherpetic Drugs in Equine Medicine

Since vaccination may not prevent disease, antiherpetic drugs have been investigated for the therapy of several equine herpesviruses. Drug efficacy has been assessed in horses with disease, but most evidence is in vitro, in other species, or empirical. Oral valacyclovir is most often administered in the therapy of equine herpesvirus type-1 (EHV-1) to protect adult horses from equine herpesvirus myeloencephalopathy, while oral acyclovir is frequently administered for EHV-5 infection in the therapy of equine multinodular pulmonary fibrosis. Other antiherpetic drugs are promising but require further investigation. Several topical drugs are also empirically used in the therapy of equine viral keratitis.

Occurrence of equine coital exanthema (ECE) in stallions in Japan and effectiveness of treatment with valacyclovir for ECE

Equine coital exanthema (ECE) has been reported in many countries, but equine herpesvirus 3 (EHV-3) has been isolated only once in Japan. In 2015, symptoms of ECE were found, and EHV-3 was isolated in two stallions. Valacyclovir, an anti-herpesvirus agent, was administered orally. The stallions rested from mating for more than two weeks, causing enormous financial losses because of their high fees. This is the first study in which valacyclovir was administered for ECE. Though valacyclovir treatment did not shorten the duration of healing, the affected area did not expand after administration of valacyclovir. Valacyclovir therefore seems to be effective for suppression of EHV-3 infection. Further investigation about the administration protocol might be required.

Antiviral agents against equid alphaherpesviruses: Current status and perspectives

Equid herpesvirus infections cause respiratory, neurological and reproductive syndromes. Despite preventive and control measures and the availability of vaccines and immunostimulants, herpesvirus infections still constitute a major threat to equine health and for the equine industry worldwide. Antiviral drugs, particularly nucleoside analogues and foscarnet, are successfully used for the treatment of human alphaherpesvirus infections. In equine medicine, the use of antiviral medications in alphaherpesvirus infections would decrease the excretion of virus and diminish the risk of contagion and the convalescent time in affected horses, and would also improve the clinical outcome of equine herpesvirus myeloencephalopathy. The combined use of antiviral compounds, along with vaccines, immune modulators, and effective preventive and control measures, might be beneficial in diminishing the negative impact of alphaherpesvirus infections in horses. The purpose of this review is to analyse the available information regarding the use of antiviral agents against alphaherpesviruses, with particular emphasis on equine alphaherpesvirus infections.

Pharmacokinetics of ganciclovir and valganciclovir in the adult horse

Equine herpes myeloencephalopathy, resulting from equine herpes virus type 1 (EHV-1) infection, is associated with substantial morbidity and mortality in the horse. As compared to other antiviral drugs, such as acyclovir, ganciclovir has enhanced potency against EHV-1. This study investigated the pharmacokinetics of ganciclovir and its oral prodrug, valganciclovir, in six adult horses in a randomized cross-over design. Ganciclovir sodium was administered intravenously as a slow bolus at a dose of 2.5 mg/kg, and valganciclovir was administered orally at a dose of 1800 mg per horse. Intravenously administered ganciclovir disposition was best described by a three-compartment model with a prolonged terminal half-life of 72 ± 9 h. Following the oral administration of valganciclovir, the mean observed maximum serum ganciclovir concentration was 0.58 ± 0.37 μg/mL, and bioavailability of ganciclovir from oral valganciclovir was 41 ± 20%. Superposition predicted that oral dosing of 1800-mg valganciclovir two times daily would fail to produce and maintain effective plasma concentrations of ganciclovir. However, superposition suggested that i.v. administration of ganciclovir at 2.5 mg/kg every 8 h for 24 h followed by maintenance dosing of 2.5 mg/kg every 12 h would maintain effective ganciclovir serum concentrations in most horses throughout the dosing interval.

Report of the Second Havemeyer EHV-1 Workshop, Steamboat Springs, Colorado, USA, September 2008

This report summarises the findings of the Second Havemeyer EHV-1 Workshop, which was held in Steamboat Springs, Colorado, USA in September 2008. A total of 38 delegates, consisting of veterinary clinicians and scientists from academia and industry participated in a series of sessions that focused on equine herpesvirus myeloencephalopathy (EHM). Each session consisted of a review, followed by short presentations on current research topics. The sessions included EHM epidemiology, in vivo and in vitro models for studying EHM, EHV-1 virulence determinants, real-time PCR diagnostics, antiviral medications and new vaccination technologies. The report summarises the key advances identified during and since the meeting. Citations are restricted to selected reviews and papers published since the workshop.