Fistulodesis Pilot Study for Closure of Perianal Fistulae

Inclusion Criteria: * All patients: * Signed informed consent * Male or female patients ≥18 years of age * Perianal fistula existing for at least 3 months * Perianal fistula that requires an examination under anaesthesia (EUA) * Women of childbearing potential must agree to use effective contraception (for details see chapter 8.6) for the duration of the trial * Women of childbearing potential: A negative pregnancy test before inclusion into the trial is required * Simple fistula, the whole fistula system must be accessible by curettage or brushing * Crohn's disease (CD) patients only: * CD diagnosis established for ≥3 months * CD in remission (Harvey-Bradshaw Index ≤4) Exclusion Criteria: * All patients: * More than 2 external fistula openings * History of irradiation of the anorectum * Acute perianal abscess. * Perianal operation during the last 4 weeks. * Known allergy or non-tolerance against either acetylcysteine, doxycycline, Evicel®, metronidazole or ciprofloxacin. * Current antibiotic therapy * Severe uncontrolled additional medical, surgical or psychiatric condition, requiring active management * Current enrollment into a clinical trial interfering with the endpoints or enrollment in another study for treatment of perianal fistula during the last 4 weeks * Inability to follow the procedures of the study, e.g. due to language problems, psychiatrical disorders, dementia, etc. of the participant, * Previous enrollment into the current study * Women who are pregnant or breastfeeding * Intention to become pregnant during the course of the study * Large pocket (≥ 1cm) within fistula tract * Horseshoe shape of the fistula tract * Superficial fistula according to clinical examination and/or ultrasound: (Male patients: Fistula tract involves less than 30% of anal sphincter apparatus, Female patients: Fistula tract involves less than 10% of anal sphincter apparatus) * Crohn's disease patients only: * Evidence of active inflammation in the rectum (besides the fistula) * Systemic intake of steroid-medication (currently or during the last 4 weeks) in a dose of \>20mg prednisone or equivalent * New immunosuppressant medication for Crohn's disease within the last 4 weeks before inclusion into the study (changes in 5-ASA medication or rectal treatment with 5-ASA or budesonide are permitted)