What are the antibiotics (atb) for cellulitis?

Antibiotic Treatment for Cellulitis

First-Line Treatment

For typical non-purulent cellulitis, start with oral antibiotics targeting beta-hemolytic streptococci—specifically penicillin, amoxicillin, dicloxacillin, or cephalexin for 5 days. 1, 2

The pathogen driving most cellulitis cases is beta-hemolytic streptococci, not Staphylococcus aureus, unless there's penetrating trauma or an underlying abscess. 1, 3 This is why streptococcal coverage alone is sufficient for most cases.

Specific Antibiotic Options:

• Penicillin 1
• Amoxicillin 1, 2
• Dicloxacillin 1, 2
• Cephalexin 1, 2, 3

For Penicillin-Allergic Patients:

• Clindamycin 1, 2
• Erythromycin 1, 2
• Levofloxacin (reserve for true beta-lactam allergies) 1, 2

Treatment Duration

Treat for 5 days initially, extending only if no improvement is seen. 1, 2 The American College of Physicians specifically recommends this 5-day course for non-purulent cellulitis. 1, 2 Research confirms that courses longer than 5 days provide no additional benefit for uncomplicated cases. 4

For severe or complicated cellulitis requiring hospitalization, extend to 7-14 days based on clinical response. 1, 2

When to Add MRSA Coverage

Add empiric MRSA coverage only for purulent cellulitis or specific high-risk features. 1, 2

Indications for MRSA Coverage:

• Purulent drainage or exudate without a drainable abscess 1
• Penetrating trauma 1, 2
• Evidence of MRSA infection elsewhere 1, 2
• Nasal MRSA colonization 1, 2
• Injection drug use 1, 2
• Systemic inflammatory response syndrome (SIRS) 1, 2

MRSA-Active Antibiotic Options:

• Clindamycin (covers both streptococci and MRSA) 1, 2
• Trimethoprim-sulfamethoxazole (must add a beta-lactam like amoxicillin for streptococcal coverage) 1, 2
• Tetracyclines (must add a beta-lactam for streptococcal coverage) 1, 2
• Linezolid (covers both streptococci and MRSA) 1, 2

Important Caveat on MRSA Coverage:

Despite high community-acquired MRSA prevalence in some regions, adding trimethoprim-sulfamethoxazole to cephalexin for non-purulent cellulitis showed no benefit in a randomized controlled trial. 5 National guidelines do not recommend routine MRSA coverage for typical non-purulent cellulitis. 3, 5 However, in areas with very high MRSA prevalence (like Hawaii with 62% MRSA isolation rates), antibiotics with MRSA activity showed significantly higher success rates. 6

Severe Cellulitis Requiring Hospitalization

For hospitalized patients, use IV vancomycin or linezolid for empiric MRSA coverage pending cultures. 2

For severely compromised patients, consider vancomycin plus piperacillin-tazobactam or a carbapenem (imipenem/meropenem) for broader coverage. 2

Adjunctive Measures

Elevate the affected extremity to promote drainage of edema and inflammatory substances. 1, 2 This is critical—failure to elevate delays improvement. 1, 2

Examine and treat interdigital toe web spaces for tinea pedis, fissuring, scaling, or maceration, as these harbor pathogens and predispose to recurrent cellulitis. 1, 2

Consider adding prednisone 40 mg daily for 7 days in non-diabetic adults to hasten resolution. 1, 2

Common Pitfalls to Avoid

• Not examining toe web spaces—this is a frequent portal of entry for pathogens 1, 2
• Failing to elevate the affected area—this significantly delays improvement 1, 2
• Stopping antibiotics at 5 days when there's no improvement—extend treatment duration in these cases 1, 2
• Routinely adding MRSA coverage for non-purulent cellulitis—this is unnecessary and promotes resistance 3, 5
• Obtaining blood cultures in typical cases—these are low-yield and not recommended unless there are severe systemic features, malignancy, or unusual predisposing factors 2