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

Cephalexin Dosing for Cellulitis

For adults with uncomplicated nonpurulent cellulitis, prescribe cephalexin 500 mg orally every 6 hours (four times daily) for 5 days. 1

Standard Dosing Regimen

• The IDSA-recommended dose is cephalexin 500 mg every 6 hours (QID) for typical cellulitis without purulent drainage or abscess. 1
• The FDA label indicates adult dosing ranges from 1-4 grams daily in divided doses, with 250 mg every 6 hours as the usual dose, though 500 mg every 12 hours may be used for skin and skin structure infections. 2
• However, the IDSA guideline specifically recommends the 500 mg QID regimen as the standard for cellulitis, which should take precedence over the FDA's broader dosing range. 1

Treatment Duration

• Treat for 5 days if clinical improvement occurs—traditional 7-14 day courses are no longer necessary for uncomplicated cases. 1
• Only extend treatment beyond 5 days if symptoms have not improved within this initial period. 1
• Do not reflexively continue antibiotics beyond 5 days without reassessing clinical response, as this is unnecessary and contributes to antibiotic overuse. 1

When Cephalexin is Appropriate

• Cephalexin is first-line therapy for typical nonpurulent cellulitis without abscess, purulent drainage, or penetrating trauma. 1
• Beta-lactam monotherapy succeeds in 96% of cellulitis cases, confirming that MRSA coverage is usually unnecessary for simple cellulitis. 1

When NOT to Use Cephalexin Alone

Do not use cephalexin monotherapy if any of the following are present: 1

• Purulent drainage or abscess
• Penetrating trauma
• MRSA risk factors (IV drug use, prior MRSA infection, recent hospitalization)

In these situations, use either clindamycin monotherapy (300-450 mg orally three times daily) OR add TMP-SMX or doxycycline to cephalexin for MRSA coverage. 1, 3

Special Circumstances

Animal or Human Bites

• Never use cephalexin for animal bites (no Pasteurella multocida activity) or human bites (no Eikenella corrodens activity)—use amoxicillin-clavulanate instead. 1

Morbidly Obese Patients

• Standard cephalexin dosing (500 mg QID) appears effective even in morbidly obese patients (BMI ≥40 kg/m²), with failure rates similar to non-obese patients (20% vs 14.5%, p=0.53). 4
• Empiric dose adjustment based solely on BMI may not be necessary. 4

High-Dose Consideration

• A pilot trial comparing high-dose (1000 mg QID) to standard-dose (500 mg QID) cephalexin showed fewer treatment failures with high-dose (3.2% vs 12.9%), though with more minor adverse effects. 5
• However, the IDSA guideline remains 500 mg QID, and high-dose regimens are not yet standard of care. 1

Critical Pitfalls to Avoid

• Never use cephalexin for purulent cellulitis without adding MRSA coverage—this is the most common error leading to treatment failure. 1
• Do not continue treatment beyond 5 days without documented lack of improvement. 1
• Do not use cephalexin for bite-related infections. 1