Clinical outcome and cyclo-oxygenase-2 expression in five dogs with solar dermatitis/actinic keratosis treated with firocoxib

Background: The conversion of arachidonic acid into prostaglandin is catalysed by the cyclo-oxygenases (COX-1/COX-2). Several studies indicate that COX-2 is overexpressed in actinic keratosis in humans and dogs. Firocoxib is a COX-2-selective inhibitor that blocks the biochemical activity of COX-2. Hypothesis/Objectives: To evaluate the efficacy of firocoxib (5 mg/kg orally once daily) for the treatment of dogs with solar dermatitis/actinic keratosis. Methods: Firocoxib 5 mg/kg was given orally once daily for 180 days to five dogs with clinical signs and histopathological lesions consistent with solar dermatitis/actinic keratosis. On days 0, 50 and 180, the severity of erythema, skin shine, induration and the number of comedones were evaluated by a clinical scoring system. On the same days, samples were collected for histopathology from 'target lesions' and COX-2 expression was evaluated by immunohistochemistry. Results: The clinical follow-up showed that four of five dogs improved with the treatment; improvement in terms of histological findings was correlated with the regularization of the epidermal proliferation rather than the recovery of dermal changes. Conclusions and clinical importance: A role for COX-2 might thus be hypothesized in the pathogenesis of canine solar dermatitis