Cephalexin Dosing for Skin Infections
For adults with skin infections, prescribe cephalexin 500 mg orally four times daily for 7-10 days, adjusting duration based on clinical response. 1
Adult Dosing Regimen
- Standard dose: 500 mg orally four times daily (QID) for 7-10 days 1, 2
- Alternative dosing: 500 mg every 12 hours is acceptable specifically for uncomplicated skin and skin structure infections 2
- The FDA-approved dosage range is 1-4 grams daily in divided doses, with 250 mg every 6 hours as the usual minimum dose 2
- For more severe infections or less susceptible organisms, higher doses may be required, but if exceeding 4 grams daily, consider parenteral cephalosporins 2
Pediatric Dosing
- Standard dose: 25-50 mg/kg/day divided into 4 doses 1, 2
- For children weighing less than 40 kg, this translates to approximately 6.25-12.5 mg/kg every 6 hours 1
- Alternative twice-daily dosing is acceptable for skin infections, dividing the total daily dose into 2 administrations 2
- Duration remains 7-10 days based on clinical response 1
Critical Clinical Considerations
Cephalexin is only effective against methicillin-susceptible Staphylococcus aureus (MSSA) and Streptococcus species 1. This is the most important caveat when prescribing this antibiotic.
When to Use Cephalexin:
- Community-acquired skin infections where MSSA is suspected 1
- Patients with non-immediate penicillin allergies (cephalexin is contraindicated in immediate hypersensitivity reactions) 1
- Pregnancy (FDA category B, generally considered safe) 1
When NOT to Use Cephalexin:
- Suspected or confirmed MRSA infections - cephalexin is completely ineffective 1
- If MRSA is suspected, use trimethoprim-sulfamethoxazole, clindamycin, or linezolid instead 1
- Research data showing clinical response to MRSA with cephalosporins 3 should be interpreted with extreme caution, as these likely represent spontaneous drainage or misdiagnosis rather than true antibiotic efficacy
Monitoring and Response
- Expect clinical improvement within 48-72 hours of starting therapy 1
- If no improvement by 72 hours, consider resistant organisms (particularly MRSA) or alternative diagnoses 1
- Complete the full 7-10 day course even if symptoms resolve earlier to prevent recurrence and resistance 1
Practical Advantages
The twice-daily dosing option (500 mg every 12 hours) offers improved convenience and compliance compared to four-times-daily regimens 2, 4, though the standard four-times-daily dosing remains the guideline-recommended approach for most skin infections 1.