Keflex (Cephalexin) Dosing for Soft Tissue Infections
For uncomplicated skin and soft tissue infections in adults, prescribe cephalexin 500 mg orally four times daily (every 6 hours) for 7 days. 1, 2
Standard Adult Dosing
- 500 mg orally every 6 hours (four times daily) is the recommended dose for mild to moderate soft tissue infections 3, 1, 2
- The FDA-approved adult dosage range is 1-4 grams daily in divided doses, with 250 mg every 6 hours as the usual dose, but 500 mg every 12 hours may be used for skin and skin structure infections 2
- Duration: 7 days is the typical treatment course, though therapy may be extended if the infection has not adequately improved 1
Pediatric Dosing
- 25-50 mg/kg/day divided into 3-4 doses (every 6-8 hours) for children 3, 2
- For skin and soft tissue infections specifically, the total daily dose may be divided and administered every 12 hours in patients over 1 year of age 2
- In severe infections, the pediatric dosage may be doubled 2
Critical Coverage Considerations
Cephalexin is only effective against methicillin-susceptible Staphylococcus aureus (MSSA) and streptococci—it does NOT cover MRSA. 1
- If MRSA is suspected (purulent infections, carbuncles, abscesses with systemic signs, or in high-prevalence communities), alternative agents such as trimethoprim-sulfamethoxazole, doxycycline, or clindamycin should be used instead 3, 1
- Clinical studies demonstrate that cephalexin achieves >90% cure rates for uncomplicated soft tissue infections when appropriate pathogens are present 4, 5, 6
When Cephalexin May NOT Be Appropriate
- Simple abscesses after adequate incision and drainage may not require antibiotics at all—a randomized trial showed 90.5% cure with placebo versus 84.1% with cephalexin in drained abscesses, even in MRSA-prevalent populations 7
- Animal or human bite wounds: Use amoxicillin-clavulanate instead due to better coverage against Pasteurella multocida and anaerobes 1
- Diabetic foot infections or complicated soft tissue infections: Broader spectrum coverage is necessary 1
- Patients with immediate hypersensitivity to penicillins: Cross-reactivity with cephalosporins is possible; consider alternative agents 1
Clinical Decision Algorithm
For patients with purulent infections (abscesses, carbuncles):
- Perform incision and drainage first 7
- If systemically well after drainage: Consider observation without antibiotics 7
- If SIRS criteria present (fever >38°C, tachycardia >90 bpm, WBC >12,000 or <4,000) or failed initial treatment: Use MRSA-active agent, NOT cephalexin 3
For non-purulent infections (cellulitis, erysipelas):
- If no risk factors for MRSA: Cephalexin 500 mg four times daily for 7 days 3, 1
- If MRSA risk factors present: Choose MRSA-active agent 3
Important Caveats
- For recurrent soft tissue infections, obtain cultures before initiating antibiotics to guide therapy 1
- The IDSA guidelines emphasize that for penicillin-allergic patients (except those with immediate hypersensitivity), cefazolin or cephalexin are appropriate alternatives to nafcillin/oxacillin 3
- Cephalexin demonstrates equivalent efficacy to fluoroquinolones for susceptible organisms, with >95% clinical response rates in comparative trials 4, 5