No effective treatment exists for papillomatosis in dogs. Azithromycin is used in humans. In this prospective, randomized, double-blind, placebo-controlled study, 17 dogs with oral (n = 12) and cutaneous (n = 5) papillomatosis were treated with azithromycin. Papillomatosis was confirmed by histopathologic examination. Ten dogs received azithromycin (10 mg/kg PO Q 24 H for 10 days), and 7 dogs received placebo. Dogs were evaluated every 5 days (at which time lesions were scored for severity) for 45 days. Skin lesions resolved in 10 to 15 days in the azithromycin-treated group. One dog in the placebo group had spontaneous remission of the lesions, but lesions were still present in the remaining 6 dogs by day 50. The azithromycin-treated dogs were followed for 8 months, during which there was no recurrence.

COMMENTARY: Dogs have at least 4 variants of oral papillomavirus, which in most cases causes a self-limiting disease. No evidence has indicated that autogenous vaccines are effective, and one study reported that skin tumors developed at the site of injection several years later. Azithromycin in this study was found to be safe and effective. The rapid and consistent resolution of the lesions within 10 to 15 days in the treatment group makes it unlikely that all the dogs had spontaneous resolution. Azithromycin is used in human medicine to treat gingival hyperplasia resulting from cyclosporine use, and I have used azithromycin successfully to treat 1 dog with this disorder. The mechanism of action is unknown, but the drug clearly has some immune-modulating and antiinflammatory properties.

Azithromycin therapy of papillomatosis in dogs: A prospective, randomized, double blinded, placebo controlled clinical trial. Yagci BB, Ural K, Ocal N, et al.
VET DERMATOL 19:194-198, 2008.