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

Abstract

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.

Diagnosis and Treatment of Primary Erythrocytosis in a Dog: A Case Report

“…This dosage, though differing from the 15mg/kg every 24 hours more commonly reported for polycythemia vera [10,14,17], obtained remission of clinical signs for over 16 months. The dog in the present case developed, however, a dermatological reaction to the medication even at this greater interval, as previously reported after prolonged use in both dogs and humans [18][19][20].…”

Macrocytosis secondary to hydroxyurea therapy

“…8 These side effects in dogs may be eliminated through the discontinuation of therapy, and/or generally avoided by adjustment of dose and frequency of hydroxyurea. 5,6,8,9 As the dog in this case report was already anemic prior to treatment with hydroxyurea, the anemia might have been multifactorial given the diarrhea and gastrointestinal blood loss. Anemia may have also developed as a side effect from the previous treatment with Palladia, as reported elsewhere 20 , and anemia of chronic disease may have also been a contributing factor.…”

“…However, reversible myelosuppression appears to be the most common hematologic toxic effect in dogs, and dogs receiving hydroxyurea develop moderate to severe anemia more frequently than other cytopenias . These side effects in dogs may be eliminated through the discontinuation of therapy, and/or generally avoided by adjustment of dose and frequency of hydroxyurea …”

“…2,3 In small animal medicine, it has mainly been used to treat primary erythrocytosis, and also pathologic thrombocytosis, hypereosinophilia, chronic myelogenous leukemia, and other neoplasms including mast cell tumors. [4][5][6][7][8][9] Hydroxyurea was first implicated as a cause of erythroid megaloblastic changes in rabbits and dogs in the early 1900s. 10 The effects of hydroxyurea on human bone marrow cell lines, and evidence of megaloblastic changes, were first described in 1966 11 , and appear to be reversible, occur at varying dosages, and are not strictly associated with anemia.…”

Hydroxyurea-induced onychomadesis in a dog with chronic myeloid leukemia: A case report

“…Hydroxyurea is a ribonucleotide reductase inhibitor that leads to decreased DNA synthesis in the S phase of the cell cycle, resulting in cell death. 1 In veterinary medicine, its clinical use covers a variety of tumor-related disorders including bone marrow disorders such as chronic granulocytic leukemia, polycythemia vera, essential thrombocythemia and hypereosinophilic syndrome; 2À6 mast cell tumors 7 and meningiomas. 8 In human patients, hydroxyurea can be used to treat sickle-cell disease, melanoma, chronic myelogenous leukemia, ovarian tumor, squamous cell carcinoma of the head and neck, renal carcinoma, bladder urothelial carcinoma, prostate carcinoma and carcinoma of the uterine cervix.…”