Is Cipro (ciprofloxacin) and Flagyl (metronidazole) effective for treating perianal fistula in the absence of fever?

From the Guidelines

Ciprofloxacin (Cipro) and metronidazole (Flagyl) can be used to treat perianal fistulas without fever, with the typical regimen being ciprofloxacin 500mg twice daily and metronidazole 500mg three times daily for 2-4 weeks, as recommended by the most recent ECCO-ESCP consensus on surgery for Crohn's disease 1. This antibiotic combination is effective because ciprofloxacin targets aerobic bacteria while metronidazole addresses anaerobic organisms, providing broad coverage for the polymicrobial infections typically found in perianal fistulas. Some key points to consider when using these antibiotics include:

• Potential side effects, such as gastrointestinal upset, metallic taste with metronidazole, and tendon issues with ciprofloxacin 1
• The importance of not taking metronidazole with alcohol
• The need for surgical intervention for definitive treatment, as antibiotics rarely lead to complete healing of the fistula on their own
• Monitoring for worsening symptoms, including development of fever, increasing pain, or spreading redness, which may indicate progression to a more serious infection requiring different management 1. It's worth noting that while there are no controlled trials showing the effectiveness of antibiotics in treating Crohn's perianal fistulas, the current clinical practice is based on uncontrolled case series and expert consensus 1. However, the most recent and highest quality study, the ECCO-ESCP consensus, recommends the use of antibiotics, including metronidazole and ciprofloxacin, in combination with seton placement for the treatment of symptomatic simple perianal fistulas 1.

From the Research

Treatment of Perianal Fistula without Fever

• The use of ciprofloxacin and metronidazole for the treatment of perianal fistulas in patients with Crohn's disease has been studied in a randomized, double-blind, placebo-controlled pilot study 2.
• The study found that remission at week 10 occurred in 3 patients (30%) treated with ciprofloxacin, no patients (0%) treated with metronidazole, and 1 patient (12.5%) treated with placebo.
• Another study found that antibiotics, including ciprofloxacin, are useful to induce a short-term response in perianal Crohn's disease, and may provide a bridging strategy to azathioprine, which seems to be essential for the maintenance of fistula improvement 3.
• 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, although the quality of evidence is low 4.

Efficacy of Ciprofloxacin and Metronidazole

• Ciprofloxacin has been shown to be effective in the treatment of a wide variety of infections, particularly those caused by Gram-negative pathogens 5.
• Metronidazole is also effective against a range of infections, including those caused by anaerobic bacteria.
• The combination of ciprofloxacin and metronidazole has been used to treat perianal fistulas in patients with Crohn's disease, with some studies suggesting that it may be effective in inducing remission and preventing fistula formation.

Safety and Tolerability

• Ciprofloxacin has been shown to be well tolerated, with no serious adverse events reported in one study 2.
• Metronidazole has also been shown to be generally well tolerated, although it can cause gastrointestinal side effects in some patients.
• The use of antibiotics, including ciprofloxacin and metronidazole, can be associated with an increased risk of Clostridioides difficile infection, although this risk can be minimized with careful prescribing and monitoring 6.