Unusual dermatological toxicity of hydroxyurea in two dogs with spontaneously occurring tumours

Hydroxyurea is a chemotherapeutic agent used to treat hypereosinophilic syndrome, mast cell tumours and many myeloproliferative disorders. It is usually well tolerated; however, reported side effects include myelosuppression and gastrointestinal complications as well as cutaneous toxicity, in very rare cases. We report the unusual appearance of onychomadesis involving several claws on all feet in two canine patients receiving long-term hydroxyurea treatment. The healing of nail lesions required cessation of treatment in one dog and dose reduction in the second animal, supporting a strict relationship between onychopathy and administration of hydroxyurea. The aim of this case report is to increase clinical awareness of dermatological toxicity associated with long-term administration of hydroxyurea.