What is the recommended dose of cephalexin (cephalosporin) for treating cellulitis in adults?

Cephalexin Dosing for Cellulitis

For adults with uncomplicated cellulitis, cephalexin 500 mg orally four times daily (every 6 hours) for 5 days is the recommended regimen, extending treatment only if clinical improvement has not occurred within this timeframe. 1, 2, 3

Standard Adult Dosing

• The FDA-approved dosing for skin and soft tissue infections is 250 mg every 6 hours, with 500 mg every 12 hours as an alternative for less severe infections. 3
• However, current IDSA guidelines specifically recommend cephalexin 500 mg every 6 hours (four times daily) as the standard regimen for cellulitis. 1
• The total daily dose ranges from 1-4 grams per day, divided into multiple doses. 3

Treatment Duration

• The standard treatment duration is 5 days if clinical improvement has occurred, with extension only if symptoms have not improved within this initial period. 2
• Traditional 7-14 day courses are no longer necessary for uncomplicated cases. 1, 2
• This shorter duration is supported by randomized controlled trial data showing no difference in outcomes between 5 and 10 days of therapy. 1

When Cephalexin is Appropriate

• Cephalexin is first-line therapy for typical nonpurulent cellulitis without abscess, purulent drainage, or penetrating trauma. 2
• Beta-lactam monotherapy (including cephalexin) is successful in 96% of cellulitis cases, confirming that MRSA coverage is usually unnecessary. 2
• Do not add MRSA coverage (such as TMP-SMX) to cephalexin for pure cellulitis without purulent features—combination therapy provides no additional benefit. 2

When NOT to Use Cephalexin Alone

• Cellulitis associated with purulent drainage, abscess, penetrating trauma, or MRSA risk factors requires either clindamycin monotherapy OR combination therapy with cephalexin plus TMP-SMX or doxycycline. 2
• Cephalexin lacks activity against MRSA and should not be used as monotherapy when MRSA coverage is indicated. 2

Pediatric Dosing

• The usual pediatric dose is 25-50 mg/kg/day divided into doses every 6 hours. 3
• For streptococcal pharyngitis and skin infections in children over 1 year, the total daily dose may be divided and given every 12 hours. 3
• For severe infections, the pediatric dosage may be doubled. 3

High-Dose Considerations

• Emerging evidence suggests high-dose cephalexin (1000 mg four times daily) may reduce treatment failure rates (3.2% vs 12.9% with standard dosing), though with more minor adverse effects. 4
• However, this high-dose regimen is not yet guideline-recommended and should be reserved for cases where standard dosing has failed or for particularly severe presentations. 4

Special Populations

• In morbidly obese patients (BMI ≥40 kg/m²), standard cephalexin dosing appears adequate—therapeutic failure rates do not differ significantly from non-obese patients (20% vs 14.5%). 5
• Empiric dose adjustment based solely on BMI is not necessary. 5

Critical Pitfalls to Avoid

• Never use cephalexin for cellulitis with purulent drainage or abscess without adding MRSA coverage—this is a common error that leads to treatment failure. 2
• Do not reflexively extend treatment beyond 5 days without reassessing clinical response—longer courses are unnecessary for uncomplicated cases. 2
• Cephalexin has no activity against Pasteurella multocida (animal bites) or Eikenella corrodens (human bites)—use amoxicillin-clavulanate instead. 1, 2