Treatment of Perianal Cellulitis
For perianal cellulitis without abscess formation, initiate oral antibiotics targeting streptococci and staphylococci; for complicated cases with abscess, perform immediate surgical drainage combined with broad-spectrum antibiotics covering Gram-positive, Gram-negative, and anaerobic organisms. 1
Initial Assessment and Classification
The critical first step is distinguishing simple perianal cellulitis from complicated infection with abscess formation:
- Simple perianal cellulitis presents with erythema, warmth, and tenderness limited to the perianal skin without fluctuance, deep tissue extension, or systemic signs 2
- Complicated perianal infection involves abscess formation, significant surrounding cellulitis extending beyond the immediate area, systemic signs (fever, elevated WBC), or immunocompromised status 1, 2
Treatment Algorithm
For Simple Perianal Cellulitis (No Abscess)
Antibiotic therapy is the primary treatment:
- First-line options: Oral beta-lactams (cephalexin) are appropriate in mild cases without MRSA risk factors in areas where community-associated MRSA is not prevalent 1
- MRSA coverage: In areas with high CA-MRSA prevalence or if MRSA is suspected, use trimethoprim-sulfamethoxazole or clindamycin as empiric therapy 3
- Duration: 5 days minimum, extending if infection has not improved 1
Specific considerations for streptococcal perianal cellulitis (particularly in children):
- Oral penicillin for 10 days is highly effective for beta-hemolytic streptococcal perianal cellulitis 4, 5
- This presentation is characterized by well-demarcated perianal erythema and may cause painful defecation 4
For Complicated Perianal Infections (With Abscess)
Surgical drainage is mandatory and takes priority:
- Perianal and perirectal abscesses require prompt surgical drainage to prevent expansion into adjacent spaces and systemic infection 1
- Incisions should be made close to the anal verge to minimize potential fistula tract length 1, 2
- The goal is to drain the abscess expeditiously and identify any fistula tract 1
Adjunctive antibiotic therapy is required when:
- Systemic signs of infection are present 1, 2
- Patient is immunocompromised 1, 2
- Source control is incomplete 1
- Significant surrounding cellulitis extends beyond the abscess 1, 2
Empiric antibiotic regimen must include:
- Broad-spectrum coverage for Gram-positive organisms (including MRSA consideration with glycopeptides if suspected) 1, 2
- Gram-negative coverage 1, 2
- Anaerobic coverage 1, 2
Special Considerations in Crohn's Disease
For perianal disease associated with inflammatory bowel disease:
- First-line: Metronidazole 400 mg three times daily and/or ciprofloxacin 500 mg twice daily 1
- Steroid-sparing agents: Azathioprine 1.5-2.5 mg/kg/day or mercaptopurine 0.75-1.5 mg/kg/day for chronic fistulating disease after excluding distal obstruction and abscess 1
- MRI and examination under anesthesia are particularly helpful for defining anatomy 1
Critical Pitfalls to Avoid
- Do not assume all perianal infections need antibiotics alone - missing an abscess that requires drainage leads to treatment failure and potential progression to necrotizing infection 2, 6
- Do not use antibiotics without drainage for abscesses - this contributes to antibiotic resistance and high recurrence rates 2
- Do not miss deeper extension - inadequate examination may fail to identify ischiorectal or supralevator involvement requiring more extensive surgical intervention 1, 2
- In areas with high CA-MRSA prevalence, avoid cephalexin monotherapy - treatment failure rates are significantly higher (74% success) compared to MRSA-active agents like trimethoprim-sulfamethoxazole (91% success) 3
Outpatient vs. Inpatient Management
- Outpatient treatment is appropriate for simple cellulitis without systemic signs, hemodynamic stability, and reliable follow-up 1, 2
- Hospitalization is indicated for systemic signs of infection, concern for deeper or necrotizing infection, immunocompromised patients, or failed outpatient therapy 1, 2