What is the first line treatment for cellulitis?

First-Line Treatment for Cellulitis

The first-line treatment for typical cellulitis is an antibiotic active against streptococci, with suitable oral options including dicloxacillin, cephalexin, clindamycin, or erythromycin. 1, 2

Antibiotic Selection Algorithm

For Non-Purulent Cellulitis (Most Common Type):

• Use antibiotics targeting streptococci, which are the most common causative pathogens 1
• Recommended oral first-line options:
  • Cephalexin 500 mg orally four times daily 2
  • Dicloxacillin 500 mg orally four times daily 1
  • Clindamycin 300-450 mg orally four times daily (for penicillin-allergic patients) 1, 2
  • Erythromycin (if local resistance patterns permit) 1

For Purulent Cellulitis or When MRSA is Suspected:

• Consider MRSA coverage if the cellulitis is associated with:
  • Purulent drainage
  • Evidence of abscess
  • Penetrating trauma
  • Injection drug use
  • Prior MRSA exposure
  • Systemic inflammatory response syndrome 2, 3
• Recommended options for MRSA coverage:
  • Trimethoprim-sulfamethoxazole 2, 4
  • Clindamycin (if local resistance patterns permit) 1, 4
  • Linezolid (for severe cases or treatment failures) 5

Duration of Treatment

• 5 days of antibiotic treatment is as effective as a 10-day course for uncomplicated cellulitis if clinical improvement occurs 1, 2
• Extend treatment if the infection has not improved within 5 days 2

Parenteral Therapy Indications

• For severely ill patients or those unable to tolerate oral medications 1
• Recommended parenteral options:
  • Nafcillin (penicillinase-resistant penicillin) 1
  • Cefazolin (first-generation cephalosporin) 1
  • Clindamycin or vancomycin (for patients with life-threatening penicillin allergies) 1

Adjunctive Measures

• Elevate the affected area to promote gravity drainage of edema and inflammatory substances 2
• Treat predisposing conditions such as tinea pedis, trauma, or venous eczema 2
• Examine interdigital toe spaces in lower extremity cellulitis to identify and treat fissuring or maceration 1, 2
• Consider systemic corticosteroids in non-diabetic adult patients to reduce inflammation and hasten resolution 1, 2, 6
• Anti-inflammatory medications like ibuprofen may help speed resolution of inflammation 6

Clinical Pearls and Pitfalls

• Blood cultures are positive in only 5% of cases and are not routinely recommended for typical cellulitis 1, 2
• Macrolide resistance among group A streptococci has increased regionally in the United States, so local resistance patterns should guide therapy 1
• Patients should show clinical improvement within 24-48 hours of starting appropriate antibiotics 2
• Failure to improve with appropriate first-line antibiotics should prompt consideration of resistant organisms or alternative diagnoses 3
• Adding trimethoprim-sulfamethoxazole to cephalexin does not improve outcomes in non-purulent cellulitis 7

Special Considerations

• Hospitalization is recommended if there is concern for deeper infection, poor adherence to therapy, severe immunocompromise, or if outpatient treatment is failing 2
• Recurrent cellulitis may require prophylactic antibiotics and aggressive management of predisposing factors 2
• S. aureus less frequently causes cellulitis unless associated with an underlying abscess or penetrating trauma 1