What is the dosing for cephalexin in treating uncomplicated cellulitis?

Cephalexin Dosing for Uncomplicated Cellulitis

For adults with uncomplicated cellulitis, cephalexin should be dosed at 500 mg orally four times daily (every 6 hours) for 5 days if clinical improvement occurs. 1, 2

Standard Adult Dosing

• The Infectious Diseases Society of America recommends cephalexin 500 mg four times daily (every 6 hours) for 5-7 days as first-line therapy for uncomplicated cellulitis. 1
• The FDA-approved dosing range for adults is 1-4 grams daily in divided doses, with 500 mg every 12 hours specifically approved for skin and skin structure infections. 2
• Treatment duration should be exactly 5 days if clinical improvement has occurred, with extension only if symptoms have not improved within this timeframe. 3, 1

Evidence Supporting This Regimen

• Beta-lactam monotherapy with cephalexin is successful in 96% of patients with typical uncomplicated cellulitis, confirming that MRSA coverage is usually unnecessary. 3
• β-hemolytic streptococci (particularly group A streptococcus) are the predominant pathogens in typical cellulitis, and cephalexin provides excellent coverage for these organisms. 1
• A large randomized trial demonstrated that adding trimethoprim-sulfamethoxazole (for MRSA coverage) to cephalexin provided no additional benefit for uncomplicated cellulitis—clinical cure occurred in 83.5% with combination therapy versus 85.5% with cephalexin alone. 1, 4

High-Dose Considerations

• A pilot randomized controlled trial evaluated high-dose cephalexin (1000 mg four times daily) versus standard-dose (500 mg four times daily), showing fewer treatment failures with high-dose (3.2% vs 12.9%) but with a higher proportion of minor adverse effects. 5
• For most patients with uncomplicated cellulitis, standard-dose cephalexin 500 mg four times daily remains appropriate. 1, 2
• Consider high-dose cephalexin (1000 mg four times daily) only for more severe infections or those caused by less susceptible organisms, though this requires further validation in larger trials. 2, 5

When Cephalexin is NOT Appropriate

• Do not use cephalexin for cellulitis associated with penetrating trauma (especially from illicit drug use), purulent drainage, or abscess—these require MRSA-active antibiotics. 1
• Cephalexin is appropriate for penicillin-allergic patients EXCEPT those with immediate hypersensitivity reactions (anaphylaxis, urticaria). 1
• If daily doses greater than 4 grams are required, parenteral cephalosporins should be considered. 2

Pediatric Dosing

• The usual recommended daily dosage for pediatric patients is 25-50 mg/kg in divided doses. 2
• For skin and skin structure infections in patients over 1 year of age, the total daily dose may be divided and administered every 12 hours. 2
• In severe infections, the pediatric dosage may be doubled. 2

Essential Adjunctive Measures

• Elevate the affected extremity above heart level to promote drainage of edema—this hastens improvement and is often neglected. 3, 1
• Treat predisposing conditions including tinea pedis, venous insufficiency, and eczema to reduce recurrence risk. 1
• Examine interdigital toe spaces for tinea pedis, fissuring, or maceration, as treating these eradicates colonization. 3

Common Pitfalls to Avoid

• Do not reflexively add MRSA coverage (trimethoprim-sulfamethoxazole or doxycycline) to cephalexin for typical nonpurulent cellulitis—this provides no additional benefit and increases adverse effects. 3, 4
• Do not extend treatment beyond 5 days if clinical improvement has occurred—traditional 7-14 day courses are no longer necessary for uncomplicated cases. 3
• Do not use cephalexin as monotherapy if MRSA risk factors are present (penetrating trauma, purulent drainage, injection drug use, known MRSA colonization). 1