The aim of this study is to evaluate the effects of rectally administered activated carbon (medical device KULIST) in chronic, uncomplicated, perianal fistulas.

Patients with chronic uncomplicated perianal fistulas located below levator ani will be treated twice daily with KULIST for 8 weeks. The efficacy will be evaluated by means of an overall clinical evaluation of fistula closure, as well as by anal ultrasonography.

Also changes in Patient Assessment of Symptoms and Impact on Daily Function will be evaluated. Safety will be evaluated by standard adverse event /adverse device effects reporting.

Inclusion Criteria:

1. Patients with perianal fistulas diagnosed by clinical examination and evaluated as "not healed/open"

2. Fistula classified as intersphincteric and transsphincteric according to Parks´classification (Parks 1976)

3. Superficial fistula involving a part of the external sphincter muscle

4. Age: ≥18 years and ≤ 75 years

5. Informed consent and/or Letter of Authority (as applicable) obtained

   Exclusion Criteria

6. Inflammatory Bowel Disease (IBD)

7. Rectovaginal fistulas

8. Rectourethral fistulas

9. Rectovesical fistulas

10. Extra-sphincteric and supra-sphincteric fistula according to Parks´classification

11. Complicated fistulas (eg. horse shoe fistulas) as evaluated by the investigator.

12. Any surgical treatment for perianal fistulas

13. Colorectal and/or anal malignancy

14. Other malignancy requiring active treatment

15. Subcutaneous fistulas not involving any part of the external sphincter

16. Other diseases which as per the investigator's opinion should be contraindicated

17. Subjects who are not able to complete study procedures as per the investigator's opinion