Treatment of Cellulitis
For uncomplicated cellulitis, the recommended first-line treatment is cephalexin 500 mg 3-4 times daily or amoxicillin-clavulanate 875/125 mg twice daily orally for 5-6 days. 1
Antibiotic Selection
First-line options:
- Cephalexin: 500 mg 3-4 times daily for 5-6 days 1
- Amoxicillin-clavulanate: 875/125 mg twice daily for 5-6 days 1
For penicillin-allergic patients:
- Clindamycin: 300-450 mg orally three times daily for 5-6 days 1
- Doxycycline: 100 mg twice daily 1
- Sulfamethoxazole-trimethoprim (160-800 mg twice daily) plus metronidazole (250-500 mg three times daily) 1
When MRSA is suspected:
Consider MRSA coverage in patients with specific risk factors including:
- Athletes
- Children
- Men who have sex with men
- Prisoners
- Military recruits
- Residents of long-term care facilities
- Prior MRSA exposure
- Intravenous drug users 2
For suspected MRSA, options include:
- Vancomycin: 15-20 mg/kg IV every 8-12 hours 1
- Linezolid: 600 mg orally every 12 hours for 10-14 days 3
- Tedizolid: 200 mg once daily for 6 days (shown to be non-inferior to linezolid in clinical trials) 4
Duration of Treatment
- Standard duration: 5-6 days for uncomplicated cellulitis 1
- Treatment should be extended if infection has not improved within 5-7 days 1
- For severe infections, treatment may need to continue for 14 days or longer 1
Assessment of Response
- Visible improvement in local signs (decreased erythema, warmth, tenderness, swelling) should be seen within 48-72 hours 1
- If no improvement is seen within 72 hours, reevaluation is necessary 1
- Patients who have received antibiotics in the previous 4-6 weeks should be given an alternative class or higher-dose regimen 1
Inpatient vs. Outpatient Management
Consider hospitalization if:
- Concern for deeper or necrotizing infection
- Poor adherence to therapy
- Infection in severely immunocompromised patients
- Outpatient treatment is failing 1
- Systemic signs of infection (fever, tachycardia, altered mental status, hemodynamic instability) 1
Discharge criteria:
- Visible improvement in local signs
- No signs of deeper or necrotizing infection
- Afebrile for at least 24 hours without antipyretics
- White blood cell count normalizing or trending toward normal 1
Transition from IV to Oral Therapy
- Transition when clinical improvement is observed and patient is afebrile
- Maintain the same antimicrobial spectrum when transitioning to oral therapy 1
- Linezolid can be switched from IV to oral at the same dose (600 mg every 12 hours) with no adjustment needed 3
Prevention of Recurrence
For patients with recurrent cellulitis (3-4 episodes per year), consider:
- Prophylactic antibiotics: oral penicillin or erythromycin twice daily for 4-52 weeks, or intramuscular benzathine penicillin every 2-4 weeks 1
- Address predisposing factors:
Special Considerations
- Immunocompromised patients: May require broader coverage and longer duration of therapy 1
- Diabetic patients: Require careful monitoring due to impaired skin barrier, immune system, and circulatory system 5
- Elderly patients: May have atypical presentations and require closer monitoring 5
- Blood cultures: Not routinely recommended but should be obtained in patients with malignancy on chemotherapy, neutropenia, severe cell-mediated immunodeficiency, immersion injuries, and animal bites 1
Common Pitfalls
Misdiagnosis: Venous stasis dermatitis, contact dermatitis, eczema, lymphedema, and deep vein thrombosis are frequently mistaken for cellulitis 6, 5
Inadequate coverage: Failing to consider MRSA in high-risk populations 2
Excessive treatment duration: Most uncomplicated cases resolve with 5-6 days of appropriate therapy 1, 2
Failure to address underlying conditions: Predisposing factors must be managed to prevent recurrence 1, 5
Missing necrotizing infections: Always evaluate for signs of deeper or necrotizing infection that require urgent surgical intervention 2, 7