Is aminoglycosides (antibiotics) as monotherapy effective for treating fistula in ano?

Aminoglycosides as Monotherapy for Fistula in Ano

Aminoglycosides should not be used as monotherapy for fistula in ano, as there is no evidence supporting their efficacy for fistula healing, and they are not the antibiotics of choice even when antibiotics are indicated.

Evidence Against Antibiotic Monotherapy for Perianal Fistulas

The most recent and highest-quality evidence comes from the 2024 ECCO Guidelines, which explicitly state that antibiotics should not be used as monotherapy for treatment of complex perianal fistulae 1. This recommendation is based on:

• Only one randomized controlled trial comparing antibiotics to placebo, which showed no significant benefit: remission occurred in 12.5% of placebo patients versus 17.6% of antibiotic-treated patients (RR: 1.41; 95% CI: 0.17–11.54) 1
• The antibiotics studied were ciprofloxacin and metronidazole—not aminoglycosides 1
• Complete healing was observed in 30% with ciprofloxacin and 0% with metronidazole, but these results were not statistically significant 1

Why Aminoglycosides Specifically Are Not Appropriate

Aminoglycosides have no established role in treating perianal fistulas for several critical reasons:

• Wrong spectrum of activity: Aminoglycosides target gram-negative bacteria and are primarily used for severe systemic infections like Pseudomonas aeruginosa, complicated UTIs, and endocarditis 2
• Significant toxicity concerns: Aminoglycosides carry substantial risks of nephrotoxicity and ototoxicity, requiring therapeutic drug monitoring when used beyond 24-48 hours 2
• Not recommended for intra-abdominal infections: Meta-analysis of 47 trials showed aminoglycosides were less efficacious than newer comparators for intra-abdominal infections, and they should not be used as first-line therapy 3
• No evidence base: There are no studies evaluating aminoglycosides specifically for perianal fistulas in the literature provided

What Antibiotics Are Actually Used (When Indicated)

When antibiotics are used for perianal disease, the evidence supports:

• Ciprofloxacin and metronidazole are the antibiotics mentioned in guidelines, though only as adjunctive therapy, not monotherapy 1
• These antibiotics may improve fistula symptoms and contribute to short-term drainage reduction when combined with anti-TNF therapy 1
• However, after discontinuation of antibiotics, benefits diminish and there is no impact on longer-term healing rates 1

The Critical Distinction: Sepsis vs. Fistula Healing

Antibiotics are indicated for perianal sepsis (abscess, acute infection) but not for fistula closure 1. This is a crucial clinical distinction:

• For anorectal abscess drainage, some evidence suggests postoperative antibiotics (metronidazole plus ciprofloxacin for 7-10 days) may reduce fistula formation rates 4
• However, other high-quality randomized trials showed no protective effect and even higher fistula rates with antibiotics (37.3% vs 22.4% placebo) 5
• These studies used ciprofloxacin/metronidazole combinations—not aminoglycosides 5, 4

Recommended Treatment Approach

For established perianal fistulas, the evidence-based treatment hierarchy is:

1. First-line: Infliximab for induction and maintenance of remission in complex perianal fistulae (EL2) 1
2. Second-line: Adalimumab for patients who fail or are intolerant to infliximab (EL3) 1
3. Surgical management: Including seton placement, advancement flaps, or other sphincter-preserving techniques 6
4. Antibiotics only as adjunctive therapy: To control active sepsis, not for fistula healing 1

Common Pitfalls to Avoid

• Do not prescribe aminoglycosides for perianal fistulas—they have no role and carry significant toxicity 2, 3
• Do not use any antibiotic as monotherapy expecting fistula closure—the evidence does not support this approach 1
• Do not confuse treatment of perianal sepsis with treatment of fistula tracts—these require different management strategies 1
• Recognize that even appropriate antibiotics (ciprofloxacin/metronidazole) only provide temporary symptom relief and do not achieve long-term fistula healing 1