Treatment of Spreading Redness (Cellulitis)
For spreading redness consistent with cellulitis, start oral antibiotics targeting streptococci immediately—penicillin, amoxicillin, dicloxacillin, cephalexin, or clindamycin are appropriate first-line choices, and a 5-day course is sufficient if clinical improvement occurs by day 5. 1
Critical First Step: Distinguish Cellulitis from Abscess
Before initiating treatment, you must determine whether this is true cellulitis (diffuse spreading infection) or a purulent collection (abscess, furuncle, septic bursitis). 1
- Cellulitis presents with diffuse erythema, warmth, swelling, and tenderness without a focal collection of pus 1
- Abscess requires drainage as primary treatment, not antibiotics alone 1
- If you see localized fluctuance, a drainable collection, or purulent material, this is NOT cellulitis—drain it first 1
Common pitfall: Calling inflammation around an abscess "cellulitis with abscess" leads to inadequate treatment. The correct approach is drainage for the abscess, with antibiotics playing only a subsidiary role. 1
Antibiotic Selection Algorithm
For Typical Uncomplicated Cellulitis (No MRSA Risk Factors):
First-line oral options (choose one): 1, 2
- Penicillin
- Amoxicillin
- Amoxicillin-clavulanate
- Dicloxacillin
- Cephalexin
- Clindamycin
The rationale: Most cellulitis is caused by streptococci (especially Group A, but also B, C, or G), and MRSA is an uncommon cause of typical cellulitis. 1 A prospective study showed 96% success with beta-lactams like cefazolin or oxacillin, confirming MRSA coverage is usually unnecessary. 1
When to Cover MRSA:
Add MRSA coverage if the patient has: 1, 2, 3
- Recent hospitalization (within 30 days)
- Previous MRSA infection
- Long-term care facility residence
- Injection drug use
- Failed first-line beta-lactam therapy after 48-72 hours
- Athletes, military recruits, prisoners, or men who have sex with men
MRSA-active oral options: 1, 2
- Clindamycin 300-450 mg every 6 hours 4
- Trimethoprim-sulfamethoxazole
- Doxycycline
Treatment Duration
5 days of antibiotics is as effective as 10 days if clinical improvement occurs by day 5. 1, 2 This is a key evidence-based recommendation that reduces unnecessary antibiotic exposure.
For streptococcal infections specifically, continue treatment for at least 10 days. 4
When Cultures Are Needed
Skip cultures for typical cellulitis. 1, 2 Blood cultures and tissue aspirates are unnecessary in straightforward cases.
Obtain blood cultures and consider tissue biopsy/aspirate if: 1, 2
- Malignancy present
- Severe systemic features (high fever, hypotension, confusion)
- Neutropenia or severe immunodeficiency
- Unusual exposures (immersion injury, animal bites, aquaculture work)
Blood cultures are positive in only 5% of cases, and needle aspirates yield organisms in 5-40% depending on technique. 1
Monitoring and Red Flags
Expect initial worsening in the first 24-48 hours. 1 Some patients deteriorate after starting antibiotics because bacterial destruction releases inflammatory enzymes—this doesn't mean treatment failure.
Reassess at 48-72 hours. If no improvement: 1, 2
- Consider MRSA coverage if not already included
- Re-evaluate for deeper infection (necrotizing fasciitis, abscess)
- Check for alternative diagnoses (venous stasis dermatitis, DVT, contact dermatitis, panniculitis) 5, 6
Signs requiring hospitalization: 2
- Systemic inflammatory response syndrome (SIRS)
- Hemodynamic instability or hypotension
- Altered mental status
- Concern for necrotizing infection
- Immunocompromised state
- Poor adherence anticipated
Adjunctive Measures
Elevate the affected area to promote drainage of edema and inflammatory mediators. 2
Address predisposing factors: 1, 7
- Treat tinea pedis and fissured toe webs (common streptococcal reservoirs for lower extremity cellulitis) 1
- Manage chronic edema from venous insufficiency or lymphatic obstruction
- Control diabetes
- Keep skin hydrated with emollients to prevent cracking 2
Consider NSAIDs: One study showed adding ibuprofen 400 mg every 6 hours for 5 days significantly shortened time to resolution (82.8% showed regression within 1-2 days versus 9.1% with antibiotics alone). 8 While not standard guideline recommendation, this may hasten recovery.
Special Anatomic Considerations
For vulvar or groin cellulitis, consider enteric flora in addition to typical gram-positive organisms, especially if near the perineum. 2 The microbial etiology may differ from cellulitis elsewhere.
For facial cellulitis, Group A Streptococcus predominates. 1
Preventing Recurrence
After the first episode, identify and treat underlying causes: 2, 7
- Chronic skin conditions (eczema, psoriasis)
- Tinea pedis
- Chronic edema
- Obesity
- Previous surgical disruption of lymphatics (saphenous venectomy, axillary node dissection, radical pelvic surgery) 1
For frequent recurrences despite addressing predisposing factors: 2, 7
- Monthly intramuscular benzathine penicillin, OR
- Daily oral penicillin V or erythromycin
Decolonization strategies (intranasal mupirocin, chlorhexidine baths, dilute bleach baths) have sparse efficacy data for preventing cellulitis recurrence. 1
Critical Pitfalls to Avoid
Don't miss necrotizing fasciitis: Widespread petechiae/ecchymoses with systemic toxicity, severe pain out of proportion to findings, or rapid progression requires immediate surgical consultation. 1, 2
Don't treat simple abscesses with antibiotics alone—drainage is mandatory. 1, 2
Don't continue ineffective antibiotics beyond 48-72 hours—reassess and adjust. 1
Don't assume all redness is infection: Venous stasis dermatitis, contact dermatitis, and DVT are common mimics. 5, 6