Anal furunculosis (perianal fistula) has an uncertain pathogenesis and a high recurrence rate. Typically, the disorder is treated palliatively with antibiotics, local hygiene, and surgery. Although cyclosporine has been shown to be effective for successfully treating similar conditions in humans (e.g., fistulous form of Crohn's disease), its major limitation is cost. This study of 24 dogs evaluated whether off-label use of cyclosporine at low doses in dogs would be effective and for how long. Dogs were randomly assigned to computer-generated groups of four and were given 1.5, 3.0, 5.0, or 7.5 mg/kg microemulsified cyclosporine once daily for 13 weeks, with follow-up at 6 and 12 months after treatment. After 13 weeks of treatment, 6 dogs were in remission (3 relapsed after 1, 2, and 6 months); 11 had improved or the condition was under control and were left untreated or received medication for an additional 1 to 3 months (4 went into remission, 7 were controlled, and 4 later relapsed); and 7 failed to respond. The response of the group receiving the highest dose was significantly better than that of all other groups combined, with most improvement noted in the first 5 weeks. Cyclosporine is a viable treatment alternative for this difficult condition and offers ease of administration and the advantage of avoiding repeated surgery and its complications.

COMMENTARY: Cyclosporine has revolutionized treatment of perianal fistula. Unfortunately, cost is still an issue. Attempts to lower the dose and save money (as in this study) are associated with higher relapse rates.

Evaluation of once daily treatment with cyclosporine for anal furunculosis in dogs. Doust R, Griffiths LG, Sullivan M. Vet Rec 152:225-229, 2003.