A randomized placebo‐controlled double‐blinded study comparing oral and subcutaneous administration of mistletoe extract for the treatment of equine sarcoid disease

Abstract Background Equine sarcoids (ES) are the most common cutaneous tumors in equids. Systemic treatment options are sparse. Subcutaneous (SC) injections of Viscum album extract (VAE) demonstrate efficacy as a systemic treatment directed against ES. Objectives/Aim To critically assess the therapeutic efficacy of orally administered VAE. Animals Forty‐five ES‐affected, privately owned, 3–12 year‐old horses. Methods A 3‐armed randomized placebo‐controlled, double‐blinded study was conducted in a double‐dummy design. Horses were subjected to oral administration and SC injections of either VAE or placebo (VAE oral/placebo SC, VAE SC/placebo oral, placebo oral/placebo SC) over a 7‐month treatment period. Primary endpoint was the change of baseline of a composite index of ES number and ES area after 14 months. Second endpoint was the clinical response. Results No statistically significant difference in the composite endpoint between the 3 study arms was found. The primary endpoint showed 4 (27%) horses in the VAE oral group with complete ES regression, 3 (21%) in the VAE SC injection group, and 2 (13%) in the placebo group. The clinical response revealed complete or partial regression in 6 horses of the oral VAE group (40%), 4 of the SC injection group (29%), and 4 of the placebo group (25%). Direct comparison of oral VAE and placebo showed an odds ratio, stratified for prognosis of 2.16 (95%‐CI: 0.45–10.42) and a P‐value of 0.336. Conclusion and Clinical Importance Oral administration of VAE is well tolerated. No statistically significant difference in the effectiveness of systemic VAE versus placebo against ES was found.