What is the typical dosing frequency of cephalexin (cephalexin) for an adult patient with uncomplicated cellulitis?

Cephalexin Dosing Frequency for Cellulitis

For uncomplicated cellulitis in adults, cephalexin should be dosed at 500 mg orally four times daily (every 6 hours) for 5 days if clinical improvement occurs. 1, 2, 3

Standard Dosing Regimen

• The recommended dose is cephalexin 500 mg orally every 6 hours (four times daily) for typical nonpurulent cellulitis in adults with normal renal function 1, 2, 3
• The FDA label confirms that for skin and skin structure infections, 500 mg may be administered every 12 hours as an alternative, though the four-times-daily regimen remains standard 3
• Treatment duration is 5 days if clinical improvement has occurred, extending only if symptoms have not improved within this timeframe 1, 2

Evidence Supporting This Regimen

• Beta-hemolytic streptococci (particularly group A streptococcus) and methicillin-sensitive Staphylococcus aureus are the predominant pathogens in typical cellulitis, and cephalexin provides excellent coverage against both 1, 2
• A large randomized trial demonstrated that adding trimethoprim-sulfamethoxazole (for MRSA coverage) to cephalexin provided no additional benefit for uncomplicated cellulitis, confirming that beta-lactam monotherapy is sufficient 2, 4
• In the per-protocol analysis of 411 patients, clinical cure occurred in 83.5% with combination therapy versus 85.5% with cephalexin alone (difference -2.0%, 95% CI -9.7% to 5.7%) 4

When Cephalexin Monotherapy Is Appropriate

• Use cephalexin alone for nonpurulent cellulitis without drainage or exudate 1, 2
• Appropriate when the patient has no MRSA risk factors (no penetrating trauma, injection drug use, purulent drainage, or known MRSA colonization) 1, 2
• Suitable for outpatients who can self-monitor with close follow-up 1

When to Modify the Regimen

• Do NOT use cephalexin monotherapy for cellulitis associated with penetrating trauma, purulent drainage, or abscess 1, 2
• For these scenarios requiring MRSA coverage, use clindamycin 300-450 mg orally four times daily as monotherapy (covers both streptococci and MRSA), or combine trimethoprim-sulfamethoxazole with a beta-lactam 1
• A pilot trial suggested that high-dose cephalexin 1000 mg four times daily had fewer treatment failures (3.2% vs 12.9%) but with more minor adverse effects, though this requires validation in larger trials 5

Essential Adjunctive Measures

• Elevate the affected extremity above heart level for at least 30 minutes three times daily to promote gravity drainage of edema 1, 2
• Examine and treat predisposing conditions including tinea pedis, venous insufficiency, and chronic edema 1, 2
• Reassess patients within 24-48 hours to verify clinical response, as treatment failure rates of approximately 20% have been reported 1

Critical Pitfall to Avoid

• Do not reflexively extend treatment to 7-10 days based on residual erythema alone, as some inflammation persists even after bacterial eradication—5 days is sufficient if clinical improvement has occurred 1, 2