Cephalexin Dosing for Soft Tissue Infections in Adults
The recommended dose of cephalexin for treating soft tissue infections in adults is 500 mg orally every 6 hours (four times daily) for 7-10 days, but this is only appropriate for non-purulent infections caused by methicillin-susceptible Staphylococcus aureus (MSSA) and streptococci. 1, 2, 3
Standard Dosing Regimen
- 500 mg orally every 6 hours (QID) is the established dose for mild to moderate skin and soft tissue infections in adults 1, 2, 4, 3
- Treatment duration is typically 7 days, with extension to 10 days based on clinical response 2, 4, 3
- The FDA-approved adult dosage range is 1-4 grams daily in divided doses 3
- For less severe infections, an alternative regimen of 500 mg every 12 hours may be used for skin and skin structure infections 3
Critical Coverage Limitations
Cephalexin does NOT cover MRSA - this is the most important clinical pitfall 1, 2, 4
When NOT to Use Cephalexin:
- Purulent infections (abscesses, carbuncles) with systemic signs or failed initial treatment - use MRSA-active agents instead 1, 2, 4
- Risk factors for MRSA including: history of MRSA colonization, injection drug use, purulent drainage, or systemic inflammatory response 4
- Necrotizing infections - these require broad-spectrum IV antibiotics and urgent surgical intervention 4
- Animal or human bites - use amoxicillin-clavulanate instead for coverage of Pasteurella multocida and anaerobes 1, 2
When Cephalexin IS Appropriate:
- Non-purulent cellulitis without systemic signs of infection 1, 4
- Impetigo caused by Staphylococcus and Streptococcus species 1
- Surgical site infections of trunk or extremity (away from axilla/perineum) 1
- Penicillin-allergic patients (except those with immediate hypersensitivity reactions) 1, 2, 4
Alternative Agents for MRSA Coverage
If MRSA is suspected, use one of these instead of cephalexin:
- Trimethoprim-sulfamethoxazole 1-2 double-strength tablets twice daily 1, 4
- Doxycycline 100 mg twice daily 1, 4
- Clindamycin 300-450 mg four times daily 1, 4
Special Clinical Situations
- Recurrent infections: Obtain cultures before starting antibiotics 2
- Diabetic foot infections: Broader spectrum antibiotics are necessary 2
- Severe infections or less susceptible organisms: Higher doses may be needed, and if >4 grams daily is required, consider parenteral cephalosporins 3
- Penicillin allergy advantage: Cephalexin offers better convenience than dicloxacillin due to suspension availability and less frequent dosing 4
Key Clinical Pearls
- Cephalexin provides excellent coverage against MSSA and streptococci, which are common pathogens in community-acquired soft tissue infections 2, 5
- Clinical response rates exceed 95% when used appropriately for susceptible organisms 5
- The drug is well-tolerated with low incidence of side effects (gastrointestinal disturbances in ~7-8% of patients) 6
- Cross-reactivity is possible in patients with immediate hypersensitivity to penicillins 2