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Objective To assess the use of concurrent ketoconazole and low dose cyclosporin administration in a group of dogs with clinical evidence of perianal fistulas, and to determine if this combination could be used to manage perianal fistulas effectively.

Design Prospective clinical trial

Procedure Sixteen dogs with clinical evidence of perianal fistulas were given ketoconazole (10 mg/kg once daily) and cyclosporin (1 mg/kg twice daily initially) for 16 weeks. Blood cyclosporin assays were performed regularly and cyclosporin doses were altered to achieve a stable blood level above 200 ng/mL. Regular examinations assessed the dogs general health, changes in clinical behaviour, fistula size and number. A complete blood count and serum biochemical analysis was performed in all dogs before and after the treatment period, and after 8 weeks of treatment in 12 dogs. Dogs were assessed for recurrence of lesions at 1, 3 and 12 months after the trial.

Results All dogs showed marked improvement in lesions and behaviour within 14 days of the medication. Fourteen dogs completed the trial. Two dogs were excluded due to concurrent disease. Thirteen dogs (93%) showed complete resolution of fistulas during the treatment period. Seven dogs (50%) had no recurrence after 12 months. Recurrence was seen in three dogs (21%) at 8, 10 and 12 months after treatment, and in three dogs (21%) within 1 month of treatment. The medication was well tolerated. Side effects included transient anorexia, vomiting and lethargy in some dogs, increased shedding of hair and gingival hyperplasia. Ketoconazole administration allowed a dramatic reduction in cyclosporin dose (over 90% in 12 dogs and 80% in the other two) compared to previously reported cases treated with cyclosporin alone.

Conclusion The use of combined ketoconazole and cyclosporin provided an effective treatment for perianal fistulas. Outcomes were similar to those seen with cyclosporin alone, but allowed a significant reduction in cyclosporin dose and, therefore, cost. The use of immunosuppressive therapy in the treatment of perianal fistulas was effective and avoided many of the problems associated with surgical treament.