What is the recommended treatment for an adult patient with cellulitis of the scalp and no significant medical history?

Treatment of Scalp Cellulitis

For an adult with uncomplicated scalp cellulitis and no significant medical history, treat with oral cephalexin 500 mg four times daily or dicloxacillin 250-500 mg every 6 hours for exactly 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 unnecessary in most cases. 1 The scalp, like other body sites, is predominantly affected by β-hemolytic streptococci (especially Streptococcus pyogenes) and methicillin-sensitive Staphylococcus aureus. 2, 3

Recommended oral regimens include:

• Cephalexin 500 mg orally every 6 hours (four times daily) 1
• Dicloxacillin 250-500 mg every 6 hours 1
• Amoxicillin (appropriate dosing) 1
• Penicillin V 250-500 mg four times daily 1

For patients with penicillin allergy, clindamycin 300-450 mg orally every 6 hours provides single-agent coverage for both streptococci and MRSA, but should only be used if local clindamycin resistance rates are less than 10%. 1

Treatment Duration

Treat for exactly 5 days if clinical improvement occurs. 1, 4 This represents a significant departure from traditional 7-14 day courses, which are no longer necessary for uncomplicated cases. 1 Extension beyond 5 days is warranted only if the infection has not improved within this initial period. 1, 4

High-quality randomized controlled trial evidence demonstrates that 5-day courses are as effective as 10-day courses for uncomplicated cellulitis. 1 Extending treatment to 10-14 days based on tradition rather than evidence increases antibiotic resistance without improving outcomes. 1

When to Add MRSA Coverage

Do NOT routinely add MRSA coverage for typical nonpurulent scalp cellulitis. 1, 4 MRSA is an uncommon cause of typical cellulitis even in hospitals with high MRSA prevalence. 1

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

• Penetrating trauma or injection drug use
• Purulent drainage or exudate
• Evidence of MRSA infection elsewhere or nasal MRSA colonization
• Systemic inflammatory response syndrome (SIRS)

If MRSA coverage is needed, use: 1

• Clindamycin 300-450 mg orally every 6 hours (monotherapy if local resistance <10%)
• Trimethoprim-sulfamethoxazole 1-2 double-strength tablets twice daily PLUS a beta-lactam
• Doxycycline 100 mg orally twice daily PLUS a beta-lactam

Essential Adjunctive Measures

Elevation of the affected area is critical and often neglected. 1, 5 While scalp elevation is less practical than limb elevation, keeping the head elevated (e.g., sleeping with head elevated on pillows) promotes gravity drainage of edema and inflammatory substances, hastening clinical improvement. 1

Examine for and treat predisposing conditions: 1, 5

• Scalp trauma or abrasions that served as portal of entry
• Seborrheic dermatitis or other chronic scalp conditions
• Poor scalp hygiene

When to Hospitalize

Hospitalization is indicated for: 1, 5, 4

• Systemic inflammatory response syndrome (SIRS): fever >38°C, tachycardia >90 bpm, tachypnea >24 rpm
• Hypotension or hemodynamic instability
• Altered mental status or confusion
• Severe immunocompromise or neutropenia
• Concern for deeper or necrotizing infection

For hospitalized patients requiring IV therapy, use cefazolin 1-2 g IV every 8 hours or nafcillin 2 g IV every 6 hours. 1, 4 If MRSA coverage is needed, vancomycin 15-20 mg/kg IV every 8-12 hours is first-line (A-I evidence). 1

Warning Signs Requiring Immediate Evaluation

Reassess within 24-48 hours to verify clinical response. 1 Treatment failure rates of 21% have been reported with some oral regimens. 1

Evaluate for necrotizing fasciitis if: 1

• Severe pain out of proportion to examination findings
• Skin anesthesia
• Rapid progression
• "Wooden-hard" subcutaneous tissues
• Systemic toxicity

If necrotizing infection is suspected, initiate broad-spectrum combination therapy (vancomycin or linezolid PLUS piperacillin-tazobactam) and obtain emergent surgical consultation. 1

Common Pitfalls to Avoid

• Do not reflexively add MRSA coverage simply because the infection involves the scalp or appears severe—beta-lactam monotherapy succeeds in 96% of typical cases. 1
• Do not extend treatment to 7-10 days based on residual erythema alone, as some inflammation persists even after bacterial eradication. 1
• Do not use doxycycline or trimethoprim-sulfamethoxazole as monotherapy for typical cellulitis, as their activity against beta-hemolytic streptococci is unreliable. 1
• Do not delay surgical consultation if any signs of necrotizing infection are present, as these progress rapidly. 1