What is the treatment for mild cellulitis?

Treatment of Mild Cellulitis

For mild, uncomplicated cellulitis, treat with oral beta-lactam monotherapy—specifically cephalexin 500 mg every 6 hours or dicloxacillin 250-500 mg every 6 hours—for 5 days, extending only if symptoms have not improved within this timeframe. 1

First-Line Antibiotic Selection

Beta-lactam monotherapy is the standard of care for typical uncomplicated cellulitis, with a 96% success rate, confirming that MRSA coverage is usually unnecessary. 1

Recommended Oral Agents

• Cephalexin 500 mg every 6 hours is the preferred first-line agent, providing effective coverage against streptococci and methicillin-sensitive S. aureus 1, 2
• Dicloxacillin 250-500 mg every 6 hours is equally effective as first-line therapy for uncomplicated cellulitis 1, 3
• Alternative options include penicillin, amoxicillin, amoxicillin-clavulanate, or clindamycin (particularly for penicillin-allergic patients, as 99.5% of S. pyogenes strains remain susceptible) 1, 4

Microbiological Rationale

• The majority of cellulitis cases (85%) are nonculturable, but when organisms are identified, most are β-hemolytic streptococci or methicillin-sensitive S. aureus 5, 6
• These pathogens are reliably covered by first-generation cephalosporins and penicillinase-resistant penicillins 1, 4

Treatment Duration

Treat for 5 days if clinical improvement has occurred; extend only if symptoms have not improved within this timeframe. 1, 4

• Five-day courses are as effective as 10-day courses for uncomplicated cellulitis 1, 4
• Traditional 7-14 day courses are no longer necessary for uncomplicated cases 1

When MRSA Coverage is NOT Needed

MRSA is an uncommon cause of typical cellulitis and routine coverage is unnecessary—do not add MRSA-active antibiotics reflexively. 1, 4

• Beta-lactam treatment succeeds in 96% of patients, confirming MRSA coverage is usually unnecessary 1
• Combination therapy with SMX-TMP plus cephalexin provides no additional benefit over cephalexin alone in pure cellulitis without abscess, ulcer, or purulent drainage 1

When to Add MRSA Coverage

Add MRSA-active antibiotics ONLY when specific risk factors are present: 1, 4

• Penetrating trauma or injection drug use 1, 4
• Purulent drainage or exudate 1, 4
• Evidence of MRSA infection elsewhere or known nasal MRSA colonization 1, 4
• Systemic inflammatory response syndrome (SIRS) with fever, tachycardia, or hypotension 1

MRSA Coverage Options (when indicated)

• Clindamycin monotherapy (covers both streptococci and MRSA, avoiding need for combination therapy) 1, 4
• SMX-TMP plus a beta-lactam (cephalexin, penicillin, or amoxicillin) 1, 4
• Doxycycline 100 mg twice daily plus a beta-lactam (never use doxycycline as monotherapy due to inadequate streptococcal coverage) 1, 4

Essential Adjunctive Measures

Elevation of the affected extremity hastens improvement by promoting gravity drainage of edema and inflammatory substances. 1, 4

Address Predisposing Conditions

• Examine interdigital toe spaces carefully for tinea pedis, fissuring, scaling, or maceration 1, 4
• Treat underlying conditions including edema, obesity, eczema, venous insufficiency, and lymphedema 1, 5
• For patients with 3-4 episodes per year despite treating predisposing factors, consider prophylactic antibiotics (oral penicillin or erythromycin twice daily for 4-52 weeks, or intramuscular benzathine penicillin every 2-4 weeks) 1

Corticosteroids (Limited Evidence)

• Systemic corticosteroids (prednisone 40 mg daily for 7 days) could be considered in non-diabetic adults, though evidence is limited 1, 4
• Avoid corticosteroids in diabetic patients 1

Monitoring and Follow-Up

Reassess within 24-48 hours for outpatients to ensure clinical improvement. 1

• If no improvement with appropriate first-line antibiotics, consider resistant organisms, cellulitis mimickers (venous stasis dermatitis, contact dermatitis, eczema, lymphedema), or underlying complications 1, 6
• Blood cultures are positive in only 5% of cases and are unnecessary for typical mild cellulitis 1

Common Pitfalls to Avoid

• Do not routinely add MRSA coverage for typical cellulitis without specific risk factors—this represents overtreatment 1, 4
• Do not extend treatment beyond 5 days automatically—only extend if clinical improvement has not occurred 1, 4
• Do not use doxycycline or trimethoprim-sulfamethoxazole as monotherapy for typical cellulitis, as their activity against beta-hemolytic streptococci is unreliable 1
• Distinguish cellulitis from purulent collections (abscesses, furuncles)—purulent collections require incision and drainage as primary treatment, not antibiotics alone 1

Hospitalization Criteria (When Mild Cellulitis Becomes Complicated)

Admit patients with any of the following: 1

• SIRS criteria (fever, altered mental status, hemodynamic instability)
• Concern for deeper or necrotizing infection (severe pain out of proportion to exam, skin anesthesia, rapid progression, bullous changes)
• Severe immunocompromise or neutropenia
• Failure of outpatient treatment after 24-48 hours
• Poor adherence to outpatient therapy