What is the treatment for a perianal skin infection?

Treatment of Perianal Skin Infection

For perianal skin infections, treatment depends critically on distinguishing between simple superficial bacterial infections (requiring antibiotics), complicated abscesses (requiring surgical drainage plus broad-spectrum antibiotics), and necrotizing infections like Fournier's gangrene (requiring emergency surgical debridement plus aggressive antimicrobial therapy). 1, 2

Initial Assessment and Classification

The first step is determining the type and severity of infection:

• Simple superficial perianal dermatitis presents with erythema, inflammation, and discomfort without abscess formation or systemic signs 3
• Perianal abscess shows induration, fluctuance, and localized pus collection 2
• Complicated perianal abscess involves significant surrounding cellulitis, deep tissue extension, multiloculation, or size >5 cm 2
• Fournier's gangrene presents with painful swelling, crepitus, skin necrosis, sepsis, and often insidious onset in diabetic or immunocompromised patients 1

Treatment Algorithm by Infection Type

Superficial Perianal Bacterial Dermatitis

For superficial perianal infectious dermatitis (classically caused by group A beta-hemolytic streptococci), oral antibiotics are the primary treatment. 3

• First-line oral therapy: Penicillinase-resistant penicillins (flucloxacillin) or cephalexin 4
• Alternative options: Erythromycin (though resistance is a concern), cefadroxil, or cefprozil 4
• Duration: 7 days is as effective as 10 days despite most trials using longer courses 4
• Topical therapy alone is insufficient for bacterial perianal dermatitis 3

Important caveat: Perianal infectious dermatitis is frequently underdiagnosed and misattributed to candidiasis, pinworms, eczema, or irritant dermatitis, leading to futile therapies 3. Bacterial culture should be obtained if the diagnosis is uncertain 3.

Simple Perianal Abscess

The primary treatment for simple perianal abscesses is incision and drainage; antibiotics are NOT typically needed in immunocompetent patients. 2

• Surgical approach: Make incisions close to the anal verge to minimize potential fistula length if one develops 2
• Post-drainage management: Internal packing is NOT necessary—evidence shows no benefit and potentially increased pain compared to no packing 5
• Antibiotics are only indicated if: Significant surrounding cellulitis, immunocompromised status, or systemic signs of infection are present 2

Complicated Perianal Abscess

Complicated perianal abscesses require both surgical drainage AND broad-spectrum antibiotic therapy. 2

Empiric antibiotic regimens for perianal/perirectal infections (covering Gram-positive, Gram-negative, and anaerobes): 1

• Metronidazole 500 mg IV every 8 hours PLUS ciprofloxacin 400 mg IV every 12 hours 1
• Alternative: Metronidazole 500 mg IV every 8 hours PLUS levofloxacin 750 mg IV every 24 hours 1
• Alternative: Ceftriaxone 1 g IV every 24 hours (provides broad coverage) 1

If MRSA is suspected (common in some geographic areas or injection drug users), add vancomycin 15 mg/kg IV every 12 hours. 1

Special consideration for injection drug users: These abscesses are polymicrobial and require evaluation for foreign bodies (radiography), vascular complications (duplex ultrasound), and endocarditis if systemic infection persists 1

Fournier's Gangrene (Necrotizing Perianal Infection)

Fournier's gangrene is a surgical emergency requiring immediate aggressive debridement plus broad-spectrum antibiotics; mortality approaches 20-50% even with treatment. 1

Immediate management priorities: 1

1. Emergency surgical debridement extending into healthy tissue—the degree of internal necrosis vastly exceeds external signs 1
2. Repeated debridements are typically necessary 1
3. Urinary diversion via suprapubic catheter 1
4. Broad-spectrum IV antibiotics covering polymicrobial flora

Recommended antibiotic regimens for necrotizing infections: 1

• Piperacillin-tazobactam 3.37 g IV every 6-8 hours PLUS vancomycin 30 mg/kg/day in 2 divided doses 1
• Alternative: Imipenem-cilastatin 1 g IV every 6-8 hours 1
• Alternative: Meropenem 1 g IV every 8 hours 1
• Alternative: Ertapenem 1 g IV daily 1
• Alternative: Cefotaxime 2 g IV every 6 hours PLUS metronidazole 500 mg IV every 6 hours PLUS clindamycin 600-900 mg IV every 8 hours 1

Fecal diversion considerations: 1

• Diverting colostomy improves outcomes by decreasing bacterial load and controlling infection 1
• Rectal diversion devices (silicone tubes) are an alternative to colostomy and can be combined with negative pressure wound therapy 1
• Avoid colostomy when other methods of fecal diversion are feasible 1

Negative pressure wound therapy (NPWT) should be considered after complete removal of necrosis to facilitate wound healing 1

Common Pitfalls to Avoid

• Do not assume all perianal abscesses need antibiotics—simple abscesses in immunocompetent patients require only drainage 2
• Do not pack abscess cavities post-drainage—evidence shows no benefit and potentially increased pain 5
• Do not delay surgical intervention for Fournier's gangrene—early aggressive debridement is critical for survival 1
• Do not miss deeper tissue involvement—imaging (CT or MRI) may be needed to define extent, particularly in obese patients where examination is difficult 1
• Do not treat perianal bacterial dermatitis with antifungals or topical steroids alone—this is a bacterial infection requiring systemic antibiotics 3
• Do not forget to culture infected tissue during surgical drainage to tailor antibiotic therapy 1