For a patient with uncomplicated left ear cellulitis, is intravenous cefazolin appropriate as first‑line therapy, and should doxycycline be added for possible MRSA or atypical coverage?

Cefazolin IV Is Appropriate for Uncomplicated Ear Cellulitis; Do Not Add Doxycycline

For uncomplicated left ear cellulitis, IV cefazolin is an excellent first-line choice, and you should NOT add doxycycline unless specific MRSA risk factors are present. 1

Why Cefazolin Alone Is the Right Choice

Beta-lactam monotherapy achieves 96% clinical success in typical cellulitis, making routine MRSA coverage unnecessary and potentially representing overtreatment. 2 The Infectious Diseases Society of America explicitly recommends penicillinase-resistant semisynthetic penicillins (like nafcillin) or first-generation cephalosporins (like cefazolin) as first-line therapy for cellulitis, with Grade A-I evidence. 1

Dosing and Duration

• Cefazolin 1–2 g IV every 8 hours is the preferred IV beta-lactam for hospitalized patients with uncomplicated cellulitis. 2
• Treat for 5 days if clinical improvement occurs; extend only if warmth, tenderness, or erythema have not improved within this timeframe. 2, 1
• Five-day courses are as effective as 10-day courses for uncomplicated cellulitis, based on high-quality randomized controlled trial evidence. 2

When You SHOULD Add MRSA Coverage (and When Doxycycline Becomes Relevant)

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

• Penetrating trauma or injection drug use 2, 1
• Purulent drainage or exudate visible on examination 2, 1
• Evidence of MRSA infection elsewhere or known nasal MRSA colonization 2, 1
• Systemic inflammatory response syndrome (SIRS): fever >38°C, tachycardia >90 bpm, hypotension, or altered mental status 2, 1
• Failure to respond to beta-lactam therapy after 48–72 hours 2

If MRSA Coverage Is Needed

If any of the above risk factors are present, your options are:

• Vancomycin 15–20 mg/kg IV every 8–12 hours (first-line for hospitalized patients, A-I evidence) 2
• Clindamycin 600 mg IV every 8 hours (only if local MRSA clindamycin resistance <10%, A-III evidence) 2
• Linezolid 600 mg IV twice daily (alternative, A-I evidence) 2
• Daptomycin 4 mg/kg IV once daily (alternative, A-I evidence) 2

Why NOT to Add Doxycycline in This Case

Doxycycline lacks reliable activity against beta-hemolytic streptococci, which are the primary pathogens in typical cellulitis. 2 The IDSA explicitly states that doxycycline must be combined with a beta-lactam when treating typical nonpurulent cellulitis, because tetracyclines have unreliable streptococcal coverage. 2

If you add doxycycline to cefazolin, you are:

1. Providing redundant coverage (cefazolin already covers streptococci and MSSA)
2. Adding unnecessary MRSA coverage when MRSA is an uncommon cause of typical cellulitis 2, 1
3. Increasing antibiotic resistance without improving outcomes 2

Never use doxycycline as monotherapy for typical cellulitis—this misses streptococcal pathogens in ~96% of cases and represents a fundamental treatment error. 2

Essential Adjunctive Measures

• Elevate the affected ear/head region to promote gravity drainage of edema and inflammatory substances. 1
• Treat predisposing conditions such as tinea pedis (if lower extremity), trauma, or venous eczema. 1
• Consider systemic corticosteroids (prednisone 40 mg daily for 7 days) in nondiabetic adult patients to potentially hasten resolution, though evidence is limited. 1

Common Pitfall to Avoid

Do not reflexively add MRSA coverage simply because the patient is hospitalized or because "it can't hurt." MRSA is an unusual cause of typical cellulitis even in high-prevalence settings, and adding unnecessary coverage increases antibiotic resistance, adverse effects, and healthcare costs without improving outcomes. 2, 1 Reserve MRSA-active agents for the specific high-risk scenarios listed above.

Monitoring and Reassessment

Reassess within 24–48 hours to verify clinical improvement. 2 If the cellulitis progresses despite cefazolin, then consider:

1. Adding empiric MRSA coverage (vancomycin or alternatives listed above) 2
2. Evaluating for abscess requiring drainage 2
3. Considering necrotizing infection if severe pain out of proportion to exam, skin anesthesia, rapid progression, or "wooden-hard" subcutaneous tissues are present 2