What is the first line treatment for cellulitis?

First-Line Treatment for Cellulitis

Cephalexin (500 mg orally 3-4 times daily for 5-6 days) is the first-line treatment for uncomplicated cellulitis targeting Streptococcus and methicillin-sensitive Staphylococcus aureus. 1

Treatment Algorithm for Cellulitis

Standard First-Line Therapy

• Cephalexin: 500 mg orally 3-4 times daily for 5-6 days
  • Recommended by the American College of Emergency Physicians as the gold standard for uncomplicated cellulitis 1
  • Effective against the most common causative organisms: β-hemolytic Streptococcus and methicillin-sensitive Staphylococcus aureus 2
  • Associated with cure rates of 90% or higher in uncomplicated cases 1

Alternative First-Line Options (for Penicillin Allergy)

• Non-Type I Penicillin Allergy:
  • Cefpodoxime, cefuroxime axetil, or cefdinir 1
• Type I (Immediate) Penicillin Allergy:
  • Clindamycin: 300-450 mg orally three times daily for 5-6 days 1
  • Provides coverage against MRSA, streptococci, and anaerobes

Special Considerations

MRSA Risk Factors

If patient has risk factors for MRSA (prior MRSA infection, frequent hospitalizations, immunocompromised status, athletes, prisoners, etc.):

• Add trimethoprim-sulfamethoxazole (1-2 DS tablets orally twice daily) or
• Switch to clindamycin (300-450 mg orally three times daily) 1, 3

Severe Infections

For more severe infections requiring parenteral therapy:

• Ceftriaxone: 50 mg/kg per day 1

Duration of Treatment

• A 5-day course of antimicrobial therapy is as effective as a 10-day course for uncomplicated cellulitis if clinical improvement occurs by day 5 1, 4
• Most patients should show improvement within 48-72 hours of starting appropriate antibiotic therapy 1

Monitoring and Follow-up

• If no improvement is seen after 72 hours:
  1. Reevaluate diagnosis
  2. Consider changing antibiotic therapy
  3. Evaluate for possible abscess formation requiring drainage 1

Important Clinical Pearls

Diagnostic Considerations

• Cellulitis is a clinical diagnosis based primarily on history and physical examination 2
• Look for acute onset of redness, warmth, swelling, tenderness, and pain 5
• Be aware of conditions that mimic cellulitis (pseudocellulitis): venous stasis dermatitis, contact dermatitis, eczema, lymphedema 5

Common Pitfalls to Avoid

1. Unnecessary MRSA coverage in areas with low MRSA prevalence 1

   • Even with rising rates of community-acquired MRSA, coverage for non-purulent cellulitis is generally not recommended 5

2. Treating for too long when shorter courses are equally effective 1, 4

   • 5 days is sufficient for most uncomplicated cases 4

3. Failing to distinguish between cellulitis and pseudocellulitis 1

4. Not performing incision and drainage for abscesses 1

   • Antibiotics alone are insufficient for abscess treatment

5. Failing to elevate the affected limb to reduce edema 1

6. Not considering underlying predisposing factors that may lead to recurrence 1, 2

Special Populations

Pediatric Considerations

• Cephalexin dosing: 25-50 mg/kg/day divided into 4 doses 1
• Avoid doxycycline in children under 8 years due to risk of tooth discoloration 1

Pregnancy Considerations

• Cephalexin is generally safe during pregnancy and breastfeeding 1
• Doxycycline is contraindicated in pregnant women in the third trimester 1

By following this evidence-based approach to cellulitis treatment, clinicians can effectively manage most cases while minimizing complications and recurrence.