What is the recommended management for facial cellulitis, including indications for hospital admission, intravenous antibiotic regimen with MRSA coverage if needed, and criteria for switching to oral therapy?

Management of Facial Cellulitis

For facial cellulitis, initiate oral beta-lactam monotherapy (cephalexin 500 mg four times daily or dicloxacillin 250-500 mg every 6 hours) for 5 days in stable outpatients without MRSA risk factors, but hospitalize immediately for IV vancomycin 15-20 mg/kg every 8-12 hours plus piperacillin-tazobactam 3.375-4.5 g every 6 hours if systemic toxicity, rapid progression, or concern for deeper infection exists. 1

Initial Risk Stratification and Admission Criteria

Hospitalize patients with facial cellulitis who exhibit any of the following:

• Systemic inflammatory response syndrome (fever >38°C, tachycardia >90 bpm, tachypnea >24 breaths/min) 1
• Hypotension or hemodynamic instability 1
• Altered mental status or confusion 1
• Severe immunocompromise or neutropenia 1
• Concern for deeper or necrotizing infection 1

Warning signs of necrotizing fasciitis requiring emergent surgical consultation include:

• Severe pain out of proportion to examination findings 1
• Skin anesthesia 1
• Rapid progression despite appropriate antibiotics 1
• "Wooden-hard" subcutaneous tissues 1
• Bullous changes or gas in tissue 1

Outpatient Antibiotic Regimen

For Typical Nonpurulent Facial Cellulitis (No MRSA Risk Factors)

Beta-lactam monotherapy achieves 96% clinical success and is the standard of care: 1

• Cephalexin 500 mg orally every 6 hours for 5 days 1
• Dicloxacillin 250-500 mg orally every 6 hours for 5 days 1
• Amoxicillin-clavulanate 875/125 mg orally twice daily for 5 days (particularly appropriate for bite-related facial cellulitis) 1

Treatment duration is exactly 5 days if clinical improvement occurs; extend only if warmth, tenderness, or erythema have not improved. 1

When to Add MRSA Coverage

Add MRSA-active antibiotics ONLY when specific risk factors are present: 1

• Purulent drainage or exudate 1
• Penetrating trauma or injection drug use 1
• Known MRSA colonization or prior MRSA infection 1
• Systemic inflammatory response syndrome 1
• Failure to respond to beta-lactam therapy after 48-72 hours 1

For facial cellulitis with MRSA risk factors, use:

• Clindamycin 300-450 mg orally every 6 hours (provides single-agent coverage for both streptococci and MRSA, but only if local MRSA clindamycin resistance is <10%) 1
• Trimethoprim-sulfamethoxazole 1-2 double-strength tablets twice daily PLUS a beta-lactam (cephalexin or amoxicillin) 1
• Doxycycline 100 mg orally twice daily PLUS a beta-lactam (never use doxycycline alone, as it lacks reliable streptococcal coverage) 1

Inpatient IV Antibiotic Regimen

For Uncomplicated Facial Cellulitis Requiring Hospitalization (No MRSA Risk Factors)

Beta-lactam monotherapy remains appropriate even in the inpatient setting: 1

• Cefazolin 1-2 g IV every 8 hours (preferred IV beta-lactam) 1
• Oxacillin 2 g IV every 6 hours (alternative) 1

For Facial Cellulitis with MRSA Risk Factors or Severe Infection

First-line MRSA-active IV therapy: 1

• Vancomycin 15-20 mg/kg IV every 8-12 hours (target trough 15-20 mg/L; A-I evidence) 1
• Linezolid 600 mg IV twice daily (equally effective alternative; A-I evidence) 1
• Daptomycin 4 mg/kg IV once daily (A-I evidence) 1
• Clindamycin 600 mg IV three times daily (only if local MRSA resistance <10%; A-III evidence) 1

For Severe Facial Cellulitis with Systemic Toxicity or Suspected Necrotizing Infection

Mandatory broad-spectrum combination therapy: 1

• Vancomycin 15-20 mg/kg IV every 8-12 hours PLUS piperacillin-tazobactam 3.375-4.5 g IV every 6 hours 1
• Linezolid 600 mg IV twice daily PLUS piperacillin-tazobactam (alternative combination) 1
• Vancomycin PLUS a carbapenem (meropenem 1 g IV every 8 hours) (alternative combination) 1
• Vancomycin PLUS ceftriaxone 2 g IV daily and metronidazole 500 mg IV every 8 hours (alternative combination) 1

Treatment duration for severe cellulitis is 7-14 days, individualized based on clinical response, with reassessment at 5 days. 1

Criteria for Switching to Oral Therapy

Transition from IV to oral antibiotics when all of the following criteria are met:

• Clinical improvement demonstrated (reduction in warmth, tenderness, and erythema) 1
• Minimum of 4 days of IV treatment completed 1
• Patient afebrile for 24-48 hours 1
• Able to tolerate oral medications 1

Appropriate oral step-down regimens:

• Cephalexin 500 mg orally every 6 hours (for non-MRSA cases) 1
• Dicloxacillin 250-500 mg orally every 6 hours (for non-MRSA cases) 1
• Clindamycin 300-450 mg orally every 6 hours (for continued MRSA coverage if local resistance <10%) 1
• Linezolid 600 mg orally twice daily (for MRSA coverage when clindamycin resistance is high, though expensive) 1

Complete the total antibiotic course (IV plus oral) to reach 7-14 days for complicated infections or 5 days for uncomplicated cases. 1

Special Considerations for Facial Cellulitis

Odontogenic Origin

For facial cellulitis suspected to originate from dental infection, amoxicillin-clavulanate 875/125 mg twice daily provides single-agent coverage for polymicrobial oral flora including anaerobes. 1

Penicillin Allergy

For patients with penicillin allergy (except immediate hypersensitivity):

• Cephalexin remains an option, as cross-reactivity is only 2-4% 1
• Avoid cephalexin in patients with confirmed immediate-type amoxicillin allergy due to identical R1 side chains 1

For severe penicillin allergy:

• Clindamycin 300-450 mg orally every 6 hours (if local MRSA resistance <10%) 1
• Levofloxacin 500 mg orally daily (reserve for beta-lactam allergies; lacks reliable MRSA coverage) 1

Adjunctive Measures

Essential non-antibiotic interventions that hasten improvement:

• Elevation of the head (if extremity involvement) or affected area above heart level for at least 30 minutes three times daily 1
• Treating predisposing conditions such as tinea pedis, venous insufficiency, and chronic edema 1
• Examining interdigital toe spaces for fissuring, scaling, or maceration and treating to reduce recurrence 1

Systemic corticosteroids (prednisone 40 mg daily for 7 days) could be considered in non-diabetic adults, though evidence is limited. 1

Mandatory Reassessment and Follow-Up

Reassess all outpatients within 24-48 hours to verify clinical response, as treatment failure rates of 21% have been reported with some oral regimens. 1

If no improvement or progression occurs after 48-72 hours of appropriate therapy:

• Reassess for MRSA risk factors 1
• Consider necrotizing infection or deeper involvement 1
• Evaluate for misdiagnosis (e.g., abscess requiring drainage) 1
• Switch to vancomycin or linezolid if MRSA is suspected 1
• Obtain emergent surgical consultation if necrotizing infection is suspected 1

Critical Pitfalls to Avoid

• Do not reflexively add MRSA coverage for all facial cellulitis—MRSA is uncommon in typical nonpurulent cellulitis even in high-prevalence settings 1
• Do not use doxycycline or trimethoprim-sulfamethoxazole as monotherapy—they lack reliable streptococcal coverage 1
• Do not delay surgical consultation if any signs of necrotizing infection are present—these infections progress rapidly and require debridement 1
• Do not continue ineffective antibiotics beyond 48 hours—progression despite appropriate therapy indicates resistant organisms or deeper infection 1
• Do not extend treatment to 10-14 days based on residual erythema alone—some inflammation persists after bacterial eradication 1