Keflex Dosing Recommendation
For most skin and soft tissue infections in adults, prescribe Keflex 500 mg every 6 hours (four times daily), as this is the FDA-approved standard dosing that optimizes pharmacodynamic targets, particularly for moderate-to-severe infections caused by Staphylococcus aureus. 1
Standard Adult Dosing
The FDA label clearly establishes the adult dosage range of 1-4 grams daily in divided doses 1. The specific regimen depends on infection severity and type:
For Mild Skin and Soft Tissue Infections:
- 500 mg every 12 hours (twice daily) is FDA-approved for uncomplicated skin and skin structure infections 1
- This simplified regimen improves adherence without compromising efficacy in mild cases 2
For Moderate-to-Severe Infections:
- 500 mg every 6 hours (four times daily) is the standard dose 1
- For infections caused by less susceptible organisms or more severe presentations, larger doses may be needed 1
- The IDSA guidelines list cephalexin 500 mg every 6 hours for surgical site infections away from axilla/perineum 3
Key Clinical Decision Points
Infection Severity Matters: While twice-daily dosing (500 mg BID) has shown equivalent efficacy to four-times-daily dosing in some studies of mild infections 2, 4, the pharmacokinetic/pharmacodynamic data suggest higher doses optimize bacterial killing, especially for S. aureus with higher MICs 5. When in doubt about severity, use the four-times-daily regimen.
Duration: Continue therapy for at least 7-10 days for most SSTIs. For streptococcal infections specifically, treat for at least 10 days 1.
Pediatric Dosing
For children, the usual recommended dosage is 25-50 mg/kg/day in divided doses 1. Recent evidence supports:
- 45 mg/kg (maximum 1.5 g) three times daily for bone and joint infections, which showed 99% cure rates with good tolerability 6
- For skin infections, the total daily dose may be divided every 12 hours 1
- In severe infections, double the dosage 1
Common Pitfalls to Avoid
Don't underdose moderate-severe infections: While twice-daily dosing is convenient and works for mild infections, moderate-to-severe SSTIs—particularly those caused by S. aureus—benefit from the higher exposure achieved with four-times-daily dosing 5. The convenience of BID dosing should not compromise outcomes in sicker patients.
Consider MRSA coverage: If there's suspicion of MRSA (community-acquired, purulent infections, treatment failure), Keflex is inappropriate. The IDSA guidelines recommend adding vancomycin or using alternative agents 3.
Maximum daily dose: If doses exceeding 4 grams daily are required, switch to parenteral cephalosporins 1.
Renal adjustment: Though not explicitly detailed in the provided evidence, cephalexin requires dose adjustment in renal impairment—verify creatinine clearance and adjust accordingly.