What antibiotics are recommended for treating rectal abscesses?

From the Guidelines

Antibiotics should be administered in patients with drained anorectal abscess in the presence of sepsis and/or surrounding soft tissue infection or in case of disturbances of the immune response, with a suggested empiric 5–10 day course of antibiotics following operative drainage to reduce the incidence of post-operative fistula. The choice of antibiotics should cover both aerobic and anaerobic bacteria, with common regimens including amoxicillin-clavulanate, or a combination of metronidazole plus either ciprofloxacin or trimethoprim-sulfamethoxazole 1. Some key points to consider when selecting an antibiotic regimen include:

• The polymicrobial nature of rectal abscesses, which typically contain a mixture of enteric gram-negative bacteria, gram-positive cocci, and anaerobes from the gastrointestinal tract
• The potential for methicillin-resistant Staphylococcus aureus (MRSA) infection, particularly in cases with risk factors for multidrug-resistant organism (MDRO) infection 1
• The importance of sampling drained pus in high-risk patients, such as those with HIV or immunocompromised patients, to guide antibiotic therapy 1
• The need for individualized treatment approaches, taking into account the patient's underlying health status, the presence of any comorbidities, and the severity of the abscess. In general, the duration of antibiotic therapy should be 7-10 days for uncomplicated cases, but may need to be extended in more complex or severe cases, such as those with significant cellulitis or immunosuppression 1.

From the Research

Recommended Antibiotics for Rectal Abscesses

The following antibiotics have been studied for their effectiveness in treating rectal abscesses:

• Piperacillin/tazobactam, cefepime, and metronidazole have been shown to provide adequate concentrations in abscess fluid, except in the largest abscesses 2
• A combination of cefotaxime and metronidazole has been found to offer the same degree of protection against post-operative infection as amoxycillin plus clavulanic acid 3
• Gentamicin + clindamycin, tobramycin + clindamycin, meropenem, imipenem, aztreonam + clindamycin, cefoxitin, cefotetan, moxalactam, cefotaxime + metronidazole, and ampicillin/sulbactam have been found to have comparable clinical success rates in intra-abdominal infections 4

Postoperative Antibiotic Use

Postoperative antibiotics have been used to prevent anal fistula formation after incision and drainage of anorectal abscesses:

• A systematic review and meta-analysis found that antibiotic therapy following incision and drainage of anorectal abscesses is associated with a 36% lower odds of fistula formation 5
• The use of antibiotics such as amoxicillin-clavulanate or ciprofloxacin for 5-10 days after operative drainage may help prevent fistula formation 5

Limitations and Considerations

The choice of antibiotic depends on the expected pathogens and resistance rate in a clinical setting 4

• The effectiveness of antibiotics such as amoxicillin-clavulanate may be limited by their inability to eradicate vaginal E coli, facilitating early reinfection 6