For a patient with right‑ear and cheek cellulitis who is only allergic to metronidazole, how many days of cephalexin should be prescribed?

Treatment Duration for Cephalexin in Right-Ear and Cheek Cellulitis

For a patient with right-ear and cheek cellulitis who is only allergic to metronidazole, prescribe cephalexin 500 mg orally four times daily for exactly 5 days, extending only if warmth, tenderness, or erythema have not improved within this timeframe. 1, 2

Evidence Supporting 5-Day Duration

• High-quality randomized controlled trial evidence demonstrates that 5-day courses achieve 98% clinical resolution at 14 days with no relapses by 28 days, equivalent to 10-day regimens for uncomplicated cellulitis 1
• The Infectious Diseases Society of America explicitly recommends 5 days as the standard duration when clinical improvement occurs (reduced warmth, tenderness, improving erythema, absence of fever) 1, 2
• Traditional 7-14 day courses are unnecessary for uncomplicated cases and promote antimicrobial resistance without improving outcomes 1

Why Cephalexin Monotherapy Is Appropriate

• Beta-lactam monotherapy achieves approximately 96% clinical success in typical non-purulent cellulitis because the primary pathogens are beta-hemolytic streptococci (especially Streptococcus pyogenes) and methicillin-sensitive Staphylococcus aureus 1, 2
• Cephalexin 500 mg four times daily provides excellent coverage against these organisms 1
• MRSA coverage is unnecessary for typical facial cellulitis even in high-prevalence settings, as MRSA is an uncommon cause 1

When to Extend Beyond 5 Days

Extend treatment only if any of the following persist after the initial 5-day course:

• Warmth at the infection site has not decreased 1
• Tenderness remains unchanged 1
• Erythema borders are stable or expanding rather than receding 1
• Fever persists (>38°C) 1

Red Flags Requiring Immediate Escalation

Do not simply extend oral therapy if any of these warning signs develop—these mandate urgent reassessment and likely hospitalization:

• Severe pain disproportionate to examination findings 1
• Rapid progression despite 48-72 hours of appropriate antibiotics 1
• Skin anesthesia, bullous changes, or "wooden-hard" subcutaneous tissue suggesting necrotizing infection 1
• Systemic toxicity (hypotension, altered mental status, confusion) 1

MRSA Coverage Is Not Needed Unless

Add MRSA-active antibiotics only if any of these specific risk factors are present:

• Penetrating trauma to the face (e.g., recent facial piercing or surgery) 1
• Visible purulent drainage or exudate 1
• Known MRSA colonization or prior MRSA infection 1
• Systemic inflammatory response syndrome (fever >38°C, heart rate >90 bpm, respiratory rate >24/min) 1
• Failure to respond to cephalexin after 48-72 hours 1

Essential Adjunctive Measures

• Elevate the head of the bed to promote gravity drainage of facial edema 1
• Treat any predisposing conditions such as chronic rhinitis, nasal vestibulitis, or facial trauma 1
• Reassess within 24-48 hours to verify clinical response, as treatment failure rates of approximately 21% have been reported with some oral regimens 1

Common Pitfalls to Avoid

• Do not automatically extend to 7-10 days based solely on residual erythema; some inflammation persists even after bacterial eradication 1
• Do not add MRSA coverage reflexively for typical facial cellulitis without the specified risk factors 1
• Do not delay surgical consultation if any signs of necrotizing infection, deep abscess, or systemic toxicity develop 1