A Phase 4 interventional study of Amoxicillin + Clavulanate and Ciprofloxacin + Metronidazole in Perianal Abscess and Anal Fistula, sponsored by University of Illinois at Chicago. Not yet recruiting at 1 site in United States. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-09-21.
Sponsored by University of Illinois at Chicago · Phase 4, Interventional, and Prevention
The goal of this clinical trial is to learn if antibiotics can prevent the formation of fistula-in-ano after incision and drainage of a first time of perianal abscess in adults. A perianal abscess is a collection of infected fluid near the anus. A Fistula-in-ano is an abnormal tunnel that can form between the anal canal and the skin after an abscess.
The main questions it aims to answer are:
Does taking antibiotics after incision and drainage of a perianal abscess lower the chance of developing a Fistula-in-ano? What medical problems or side effects do participants have after taking antibiotics or not taking antibiotics?
Researchers will compare participants who recieve antibiotics after abscess drainage with paticipants who do not recieve antibiotics after abscess drainage, to see if antibiotics lower the chance of developing a Fistula-in-ano.
Participants will:
Be randomly assigned to recieve antibiotics for 7 days after abscess incision and drainage or to not recieve antibiotics after abscess incision and drainage.
Attend follow-up clinic visits after incision and drainage as part of their standard of care.
Complete follow-up phone call about 12 months after incision and drainage. Allow the study team to review their medical record for abscess treatment, symptoms, recurrence, fistula-in-ano formation, additional procedures, and antibiotics side effects.
This is a single-center, randomized, open-label clinical trial evaluating whether a 7-day course of postoperative antibiotics after standard of care incision and drainage of a first-time perianal abscess reduces subsequent anal fistula formation compared with no postoperative antibiotics.
Perianal abscess is a common anorectal condition treated primarily with incision and drainage. After drainage, some patients later develop an anal fistula, which is an abnormal tract between the anal canal and the perianal skin. The role of routine antibiotics after adequate drainage remains uncertain, especially in patients without high-risk clinical features that would otherwise require antibiotics as part of standard care. This study is designed to evaluate whether a short postoperative antibiotic course can reduce fistula formation after a first episode of perianal abscess.
Eligible adult participants with a first-time perianal abscess requiring incision and drainage will be randomized in a 1:1 ratio to either postoperative antibiotics or no postoperative antibiotics. Participants assigned to the antibiotic arm will receive amoxicillin/clavulanate for 7 days. Participants with penicillin allergy may receive ciprofloxacin plus metronidazole instead. Participants assigned to the no-antibiotic arm will not receive postoperative antibiotics unless antibiotics are later determined to be medically necessary by the treating clinician.
All participants will receive standard clinical care for the perianal abscess, including incision and drainage as determined by the treating surgical team. The study does not change the technical approach to drainage or other clinically indicated care. The research intervention is the randomized postoperative antibiotic strategy.
Participants will be followed through routine clinical visits and a 12-month follow-up phone call. The study will collect information from the medical record and follow-up contacts regarding fistula formation, recurrent abscess, additional procedures or treatment, emergency department visits or readmissions, antibiotic use, medication adherence, and antibiotic-related adverse events. The findings may help clarify whether routine postoperative antibiotics should be used after drainage of first-time perianal abscess in patients without other clinical indications for antibiotics.
169 studies on the registry are indexed under Rectal Fistula; 45 are open to participants now.
This study's planned enrollment of 236 is above the median of 66 across 115 interventional studies indexed under Rectal Fistula.
Browse Rectal Fistula studies →University of Illinois at Chicago is the lead sponsor of 506 studies on the registry; 120 are open to participants now.
Of its 32 completed or terminated interventional studies of FDA-regulated products, 19 (59%) have results posted.
Counted across the registry records on this site, refreshed daily.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Cancer (malignancy)
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Immunosuppression
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Corticosteroids (steroids)
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
HIV
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Clinically significant
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Contraindication
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Participants assigned to this arm will receive antibiotics for 7 days after standard of care incision and drainage of a first-time perianal abscess. The planned antibiotic regimen is amoxicillin/clavulanate. Participants with penicillin allergy may receive ciprofloxacin plus metronidazole instead.
Drug: Amoxicillin + Clavulanate · Drug: Ciprofloxacin + Metronidazole
Participants randomized to this arm will not receive postoperative antibiotics after standard of care incision and drainage, unless antibiotics are later determined to be clinically necessary by the treating clinician. Any antibiotic use after randomization will be recorded, and participants may continue study follow-up unless they withdraw or the study team determines that stopping participation is necessary for safety.
Drug pages: Amoxicillin · Clavulanic Acid
Participants assigned to the antibiotics after incision and drainage arm will receive amoxicillin/clavulanate 875/125 mg by mouth twice daily for 7 days after standard of care incision and drainage.
Drug pages: Ciprofloxacin · Metronidazole
Participants assigned to the antibiotics after incision and drainage arm who have a penicillin allergy may receive ciprofloxacin 500 mg by mouth twice daily plus metronidazole 500 mg by mouth three times daily for 7 days after standard of care incision and drainage.
Number of participants who develop fistula in ano within 6 months after incision and drainage
Anal fistula formation will be assessed as a binary outcome for each participant. Fistula will be defined as documentation of a clinically diagnosed anal fistula during follow-up, based on clinical examination, imaging, operative or procedure findings, or medical record documentation.
Time frame: 6 months after incision and drainage
Number of participants who develop Fistula in Ano within 12 months after incision and drainage
Anal fistula formation within 12 months will be assessed as a binary outcome for each participant. Participants will be counted as having developed a Fistula in Ano if a clinically diagnosed anal fistula is documented within 12 months after incision and drainage. Documentation may be based on clinical examination, imaging, operative or procedure findings, medical record review, or participant report during the 12-month follow-up phone call and confirmed by clinical documentation when available.
Time frame: 12 months after incision and drainage
Number of participants who develop recurrent perianal abscess within 12 months after incision and drainage.
Recurrent perianal abscess will be assessedas a binary outcome for each participant. Recurrent perianal abscess will be defined as documentation of a new or recurrent perianal abscess during follow-up, including clinical diagnosis, emergency department visit, clinic visit, imaging, or need for repeat drainage or procedure.
Time frame: 12 months after incision and drainage
Number of participants who require an additional abscess or fistula related procedure or intervention within 12 months after incision and drainage.
The need fo additional procedure or intervention will be assessed as a binary outcome for each participant. Participants will be counted as requiring an addictional procedure or intervention if any abscess or fistula related procedure is documented within 12 months after incision and drainage. Procedures may include repeat incision and drainage, examination under anesthesia, seton placement, fistulotomy, fistula repair, or other abscess or fistula related intervention documented in the medical record.
Time frame: 12 months after incision and drainage
Number of participants with an abscess or fistula emergency department visit or hospital readmission within 12 months after incision and drainage.
Emergency department visits or hospital readmissions will be assessed as a composite binary outcome for each participant. Participants will be counted in this outcome if they have at least one emergency department visit or at least one hospital readmission related to perianal abscess, fistula, wound infection, worsening symptoms, recurrent abscess, or complications of the assigned postoperative management strategy within 12 months after incision and drainage. Events will be identified through medical record review and follow-up assessments.
Time frame: 12 months after incision and drainage
Number of participants with antibiotic adverse events by event type within 30 days after incision and drainage.
Antibiotic adverse events will include medication side effects or complications, documented during follow-up or through medical record review. These include nausea, vomiting, diarrhea, rash, allergic reaction, yeast infection, clostridioides difficile infection, tendon symptoms, neurologic symptoms, liver-related symptoms, or other adverse events attributed to antibiotic therapy. Adverse event will be summarized by event type. The number of participants with each adverse event type will be reported. A participant may be counted in more than one adverse event type if multiple events occur.
Time frame: Within 30 days after incision and drainage
Plan to share: No — Individual participant data will not be made publicly available. Aggregate study results will be reported as required and may be published in scientific presentations or manuscripts.
This study is not yet recruiting, as verified in Jun 2026. You cannot join it, but the record below documents what was studied.
Get an email when the registry record changes — status, dates, results — or when someone posts here.
Sign in to followQuestions and observations about this study, from anyone following it. Not medical advice, and not a channel to the study team — their contact details are on the registry record.
Sign in to join the discussion. Reading takes no account; posting does. You choose a display name, and a pseudonym is the default.
Nothing here yet. If you are running this trial, taking part in it, or weighing whether to, this is the place to say so.
Studies of the drugs tested here: Amoxicillin · Clavulanic Acid · Ciprofloxacin · Metronidazole
University of Illinois at Chicago →