Perianal Fistula: How Much Cyclosporine?

Canine perianal fistula disorder is a chronic, progressive disease characterized by ulceration of the perianal tissue. Common clinical signs include tenesmus, dyschezia, constipation, and mucopurulent discharge from the perineum. Evidence is accumulating that the disorder is immune mediated, so cyclosporine is increasingly being used as the treatment of first choice. In this study, 20 dogs with perianal fistula were randomly assigned to 1 of 2 modified-cyclosporine treatment groups (2 mg/kg or 5 mg/kg, both given once daily for 8 weeks). Concurrent ketoconazole was not used in this study. Dogs were evaluated every 2 weeks, and the lesions were photographed. Response to treatment was evaluated by measurement of lesion surface area, a visual analog scale, and the presence and severity of clinical signs. Both groups of dogs benefited from therapy after 8 weeks of treatment; however, dogs receiving 5 mg/kg improved faster. Clinical signs and lesions resolved in both groups but resolution levels were higher in the dogs receiving 5 mg/kg.

COMMENTARY: Traditionally, perianal fistula has been considered a "surgical" disease. However, increasing evidence suggests that this condition may be best managed as a chronic skin disease, with surgery as an adjunct rather than primary treatment. Care must be taken when comparing response to treatment in studies of perianal fistula because the earlier studies used nonmodified cyclosporine. A common treatment approach is to use concurrent ketoconazole to increase serum concentrations of cyclosporine, thereby allowing a lower dose of the latter to be used. In our hospital, ketoconazole (8 mg/kg) and cyclosporine (5 mg/kg) once daily are used as an initial treatment protocol for perianal fistula. Initial response may be seen within a few weeks, but maximal response may require up to 16 weeks of therapy. Tacrolimus ointment can also be used concurrently in these dogs.

Evaluation of the effect of two dose rates of cyclosporine on the severity of perianal fistulae lesions and associated clinical signs in dogs. House AK, Guitian J, Gregory SP, Hardie R. J VET SURG 35:543-549, 2006.