Topical use of 5% acyclovir cream for the treatment of occult and verrucous equine sarcoids: a double-blinded placebo-controlled study

BACKGROUND: Previous studies mention the use of topical acyclovir for the treatment of equine sarcoids. Success rates vary and since the bovine papillomavirus (BPV) lacks the presence of a kinase necessary to activate acyclovir, there is no proof of its activity against equine sarcoids. RESULTS: Twenty-four equine sarcoids were topically treated with acyclovir cream and 25 with a placebo. Both creams were applied twice daily during 6 months. Before the start of the treatment and further on a monthly basis, photographs and swabs were obtained. On the photographs, sarcoid diameter and surface area were measured and verrucosity of the tumours was quantified using a visual analog scale (VAS). The swabs were analysed by PCR for the presence of BPV DNA and positivity rates were calculated as the number of positive swabs divided by the total number of swabs for each treatment group at each time point. Success rates were not significantly different between both treatment groups. There was also no significant effect of treatment on sarcoid diameter, surface area or VAS score. For the swabs, a significantly higher BPV positivity rate was found for acyclovir treated tumours compared to placebo treated sarcoids only after 1 month of treatment and not at other time points. CONCLUSIONS: None of the results indicate that treatment with acyclovir yields any better results compared to placebo treatment.