What is the antibiotic (Abx) of choice for cellulitis?

First-Line Antibiotic Therapy for Cellulitis

For typical uncomplicated cellulitis, a beta-lactam antibiotic active against streptococci such as penicillin, amoxicillin, dicloxacillin, or cephalexin is the treatment of choice. 1

Pathogen Considerations

• Cellulitis is most commonly caused by streptococci (often group A, but also groups B, C, or G), with Staphylococcus aureus being a less frequent cause unless associated with penetrating trauma or abscess 1
• The source of streptococci is often unclear but may originate from macerated interdigital toe spaces, emphasizing the importance of treating underlying tinea pedis 1
• MRSA is an unusual cause of typical cellulitis without abscess or purulent drainage 1

First-Line Treatment Options

Oral Therapy (for mild to moderate cases):

• Penicillinase-resistant semisynthetic penicillin (e.g., dicloxacillin) 1
• First-generation cephalosporin (e.g., cephalexin) 1
• Clindamycin (for penicillin-allergic patients) 1
• Erythromycin (though macrolide resistance among group A streptococci has increased regionally in the US) 1

Parenteral Therapy (for severe cases or patients unable to tolerate oral medications):

• Nafcillin (penicillinase-resistant penicillin) 1
• Cefazolin (first-generation cephalosporin) 1, 2
• Clindamycin or vancomycin (for patients with life-threatening penicillin allergies) 1

Special Considerations

MRSA Coverage

• Not routinely needed for typical cellulitis 1
• Consider MRSA coverage (vancomycin, linezolid, daptomycin, telavancin, or ceftaroline) only if: 1
  • Cellulitis is associated with penetrating trauma
  • Evidence of MRSA infection elsewhere
  • Nasal colonization with MRSA
  • History of injection drug use
  • Presence of systemic inflammatory response syndrome (SIRS)

Duration of Therapy

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

Treatment Failure Considerations

• Patients slow to respond may have deeper infection or underlying conditions (diabetes, venous insufficiency, lymphedema) 1
• Consider blood cultures and tissue aspirates/biopsies in patients with malignancy, severe systemic features, or unusual predisposing factors 1

Adjunctive Measures

• Elevation of the affected area to promote gravity drainage of edema and inflammatory substances 1
• Treatment of predisposing conditions (tinea pedis, venous eczema, trauma) 1
• Systemic corticosteroids (e.g., prednisone 40 mg daily for 7 days) could be considered in non-diabetic adult patients with cellulitis to hasten resolution 1

Prevention of Recurrence

• Identify and treat predisposing conditions such as edema, obesity, eczema, venous insufficiency, and toe web abnormalities 1
• For patients with 3-4 episodes per year despite addressing predisposing factors, consider prophylactic antibiotics (oral penicillin or erythromycin twice daily for 4-52 weeks, or intramuscular benzathine penicillin every 2-4 weeks) 1

Common Pitfalls to Avoid

• Unnecessarily adding MRSA coverage for typical cellulitis - a study showed that treatment with beta-lactams like cefazolin or oxacillin was successful in 96% of patients with cellulitis 1
• Adding trimethoprim-sulfamethoxazole to cephalexin did not improve outcomes for uncomplicated cellulitis 3
• Prolonging antibiotic therapy beyond 5 days when clinical improvement has occurred 1
• Failing to address underlying predisposing conditions that may lead to recurrence 1