What is the recommended IV (intravenous) antibiotic regimen for the treatment of cellulitis?

IV Antibiotic Regimen for Cellulitis

For non-purulent cellulitis requiring IV therapy, vancomycin or another antimicrobial effective against both MRSA and streptococci is recommended as the first-line treatment, particularly in patients with risk factors for MRSA. 1

Initial Antibiotic Selection Algorithm

Severity-Based Approach

Mild to Moderate Cellulitis (non-purulent):

• First-line options:
  • Cefazolin 1-2 g IV every 8 hours 1, 2
  • Nafcillin/Oxacillin 1-2 g IV every 4-6 hours 1, 2

Moderate to Severe Cellulitis (non-purulent with SIRS, MRSA risk factors, or penetrating trauma):

• First-line options:
  • Vancomycin 15-20 mg/kg IV every 8-12 hours 1, 2
  • Daptomycin 4 mg/kg IV once daily 3

Severe Cellulitis or Severely Immunocompromised:

• Combination therapy:
  • Vancomycin plus piperacillin-tazobactam 1
  • Vancomycin plus imipenem/meropenem 1

Risk Factors for MRSA Coverage Consideration

• Prior MRSA infection or colonization
• Penetrating trauma
• Injection drug use
• SIRS (Systemic Inflammatory Response Syndrome)
• Athletes, prisoners, military recruits
• Residents of long-term care facilities 2, 4

Duration of Therapy

• Standard duration: 5 days 1
• Extend treatment if infection has not improved within 5 days 1
• Factors associated with longer treatment duration:
  • Advanced age
  • Elevated C-reactive protein levels
  • Diabetes mellitus
  • Concurrent bloodstream infection 5

Monitoring Response to Treatment

• Evaluate for improvement within 48-72 hours
• Clinical improvement typically occurs within 2-3 days of initiating appropriate therapy 6
• Consider treatment failure if no improvement after 48-72 hours

Alternative Regimens

• Once-daily regimens for outpatient therapy:
  • Cefazolin 2 g IV once daily plus oral probenecid 1 g (equivalent efficacy to ceftriaxone) 7, 6
  • Ceftriaxone 1-2 g IV once daily 7

Special Considerations

Pediatric Patients

For children with cellulitis requiring IV therapy:

• Age 8-21 days: Ampicillin IV (150 mg/kg/day divided q8h) plus ceftazidime or gentamicin
• Age 22-28 days: Ceftriaxone IV (50 mg/kg/day)
• Age 29-60 days: Ceftriaxone IV (50 mg/kg/day) 1

Risk Factors for Treatment Failure

• Chronic venous disease (4.4 times higher risk of failure with cefazolin/probenecid regimen) 8
• Diabetes mellitus 5
• Advanced age 5

Supportive Measures

• Elevation of the affected area 1
• Treatment of predisposing factors (edema, underlying skin disorders) 1
• Careful examination of interdigital toe spaces in lower-extremity cellulitis 1

Indications for Hospitalization

• SIRS
• Altered mental status
• Hemodynamic instability
• Concern for deeper or necrotizing infection
• Poor adherence to therapy
• Severe immunocompromise
• Failure of outpatient treatment 1

Transitioning to Oral Therapy

• Consider switch to oral therapy after clinical improvement with IV antibiotics
• Ensure appropriate coverage of identified or suspected pathogens
• Maintain the same antimicrobial spectrum when transitioning to oral therapy

Remember that blood cultures are not routinely recommended for typical cases of cellulitis but should be obtained in immunocompromised patients or those with systemic symptoms 2, 4.