| E.1 Medical condition or disease under investigation | 
| E.1.1 | Medical condition(s) being investigated |  | 
| E.1.1.1 | Medical condition in easily understood language |  | 
| E.1.1.2 | Therapeutic area | Diseases [C] - Digestive System Diseases [C06] | 
| MedDRA Classification | 
| E.1.3 | Condition being studied is a rare disease | No | 
| E.2 Objective of the trial | 
| E.2.1 | Main objective of the trial | 
| The objective of this trial is to establish if adding antibiotic treatment to surgical drainage of perianal abscess results in less perianal fistulas. |  | 
| E.2.2 | Secondary objectives of the trial | 
| Quality of life at 12 months measured with the EQ-5D-5L with Dutch rating. In-hospital direct and indirect costs and out-of hospital postoperative costs, need of repeated drainage, patient related outcome (PRO) and clinical outcome measures. |  | 
| E.2.3 | Trial contains a sub-study | No | 
| E.3 | Principal inclusion criteria | 
| In order to be eligible to participate in this study, a subject must meet all of the following criteria: -	Men and women aged 18 years or older
 -	Eligible for e-mail questionnaires
 -	Sufficient understanding of the Dutch written language (reading and writing)
 -	Obtained written informed consent
 
 |  | 
| E.4 | Principal exclusion criteria | 
| -	A coexistent perianal fistula -	Spontaneous drainage
 -	Secondary or recurrent perianal abscess
 -	Presence of an internal fistula opening
 -	Any additional surgical procedure performed during the same session
 -	Previous (peri)anal surgery
 -	Inflammatory bowel disease
 -	History of radiation of the pelvic area
 -	Anorectal malignancy
 -	Immunodeficiency
 -       Kidney failure, eGFR <30ml/min
 -	Valvular heart disease
 -	Pregnancy or lactation
 -	Antibiotic prophylaxis indicated for another reason
 -	Immunosuppressive medication at the time of surgery
 -	Allergy to metronidazole or ciprofloxacin
 -       Not able or trouble with swallowing pills
 -	Concomitant use of: tizadine, theopylline clozapine, olanzapine, pirfenidone, carbamazepine, agomelatine, amiodarone, erytromcyine, sotalol, azithormycine, citalopram, escitalopram, flecainide, fluconazol, haloperidol >5mg/day, methadone, ondansetron, lithium, lopinavir/ritonavir, ritonavir capsules, temsirolimus, disulfiram, mebendazole, corticosteroids
 |  | 
| E.5 End points | 
| E.5.1 | Primary end point(s) | 
| Primary outcome measure is development of a perianal fistula. A perianal fistula is diagnosed based on findings from physical examination. An external opening with or without serosanguilent discharge is considered a fistula. In case of doubt an endoanal ultrasonography or MRI is performed. |  | 
| E.5.1.1 | Timepoint(s) of evaluation of this end point |  | 
| E.5.2 | Secondary end point(s) | 
| -	Quality of life at 12 months measured with the EQ-5D-5L with Dutch rating. The EQ-5D-5L is a generic Health Related Quality of Life (HRQoL) measure, which is broadly used in economic evaluation. The instrument examines a patient’s HRQoL on the day of the interview. It consists of the EQ-5D-5L descriptive system and the EQ-Visual Analogue Scale. The descriptive system comprises five dimensions: mobility, self-care, usual activities, pain/discomfort and anxiety/depression. Each dimension has five levels: no problems, slight problems, moderate problems, severe problems, and extreme problems. Responses to the 5 items result in a patient’s health state that can be transformed into an index score representing health-related quality of life, ranging between 0 (death) and 1 (full health). These index scores are combined with length of life to calculate the QALY. The EQ-VAS records the patient’s self-rated health with endpoints labelled ‘the best health you can imagine’ at the top and ‘the worst health you can imagine’ at the bottom. -	In-hospital direct and indirect costs (measured with iPCQ and iMCQ) and out-of hospital postoperative costs.
 -	Need of repeated drainage.
 -	Patient related outcome (PRO) are complaint reduction assessed by a proctology specific validated patient-related outcome measure, the proctoPROM(13). This was recently developed and validated at Proctos Clinic. At baseline participants will complete PRO questionnaires. Also at 1 and 6 weeks and 6 and 12 months participants will fulfill the PRO questionnaires. These will be send to them by email with access to a web tool (Castor). If the patient does nog have an email account, the questionnaires will be send the patients’ home address, accompanied by a return envelope provided with postage stamps and the address of the hospital.
 -	Clinical outcome measures;
 o	Data collected during operation include are code(s) of surgeon(s); date of surgery; type of surgery; blood loss in milliliters; ‘skin to skin’ operation time; intraoperative complications.
 o	The following postoperative parameters are collected:
 	Day of discharge from hospital;
 	Complications (postoperative bleeding, urinary retention, emergency reoperation, anal stenosis and fecal incontinence) including death and cause of death, early complications are complications manifested within 7 days post procedure. Complications are considered late complications at 52 weeks (1 year) post-procedure. Early complications include ‘abscess’ and ‘urinary retention’ and will be assessed 7 days post-procedure. ‘Abscess’ will be assessed by physical examination and ‘urinary retention’ by ultrasonography ; further
 	Reason and duration of possible readmission in hospital within 90 days postoperatively.
 	Duration of absence from work.
 |  | 
| E.5.2.1 | Timepoint(s) of evaluation of this end point | 
| PROM at 1 and 6 weeks and 6 and 12 months Early complications are complications manifested within 7 days post procedure. Complications are considered late complications at 52 weeks (1 year) post-procedure.
 |  | 
| E.6 and E.7 Scope of the trial | 
| E.6 | Scope of the trial | 
| E.6.1 | Diagnosis | No | 
| E.6.2 | Prophylaxis | Yes | 
| E.6.3 | Therapy | No | 
| E.6.4 | Safety | No | 
| E.6.5 | Efficacy | No | 
| E.6.6 | Pharmacokinetic | No | 
| E.6.7 | Pharmacodynamic | No | 
| E.6.8 | Bioequivalence | No | 
| E.6.9 | Dose response | No | 
| E.6.10 | Pharmacogenetic | No | 
| E.6.11 | Pharmacogenomic | No | 
| E.6.12 | Pharmacoeconomic | No | 
| E.6.13 | Others | No | 
| E.7 | Trial type and phase | 
| E.7.1 | Human pharmacology (Phase I) | No | 
| E.7.1.1 | First administration to humans | No | 
| E.7.1.2 | Bioequivalence study | No | 
| E.7.1.3 | Other | No | 
| E.7.1.3.1 | Other trial type description |  | 
| E.7.2 | Therapeutic exploratory (Phase II) | No | 
| E.7.3 | Therapeutic confirmatory (Phase III) | No | 
| E.7.4 | Therapeutic use (Phase IV) | Yes | 
| E.8 Design of the trial | 
| E.8.1 | Controlled | Yes | 
| E.8.1.1 | Randomised | Yes | 
| E.8.1.2 | Open | No | 
| E.8.1.3 | Single blind | No | 
| E.8.1.4 | Double blind | Yes | 
| E.8.1.5 | Parallel group | No | 
| E.8.1.6 | Cross over | No | 
| E.8.1.7 | Other | No | 
| E.8.2 | Comparator of controlled trial | 
| E.8.2.1 | Other medicinal product(s) | No | 
| E.8.2.2 | Placebo | Yes | 
| E.8.2.3 | Other | No | 
| E.8.2.4 | Number of treatment arms in the trial | 2 | 
| E.8.3 | The trial involves single site in the Member State concerned | No | 
| E.8.4 | The trial involves multiple sites in the Member State concerned | Yes | 
| E.8.4.1 | Number of sites anticipated in Member State concerned | 8 | 
| E.8.5 | The trial involves multiple Member States | No | 
| E.8.6 Trial involving sites outside the EEA | 
| E.8.6.1 | Trial being conducted both within and outside the EEA | No | 
| E.8.6.2 | Trial being conducted completely outside of the EEA | No | 
| E.8.7 | Trial has a data monitoring committee | Yes | 
| E.8.8 | Definition of the end of the trial and justification where it is not the last
                        visit of the last subject undergoing the trial |  | 
| E.8.9 Initial estimate of the duration of the trial | 
| E.8.9.1 | In the Member State concerned years |  | 
| E.8.9.1 | In the Member State concerned months |  | 
| E.8.9.1 | In the Member State concerned days |  |