Cephalexin Dosing for Adult Skin Infections
For adults with skin and soft tissue infections, cephalexin should be dosed at 500 mg orally four times daily (every 6 hours), with treatment duration of 7-10 days depending on clinical response.
Standard Dosing Regimen
The Infectious Diseases Society of America (IDSA) guidelines and FDA labeling establish clear dosing parameters for cephalexin in adult skin infections:
- Standard dose: 500 mg orally four times daily (QID) 1, 2
- Alternative dosing: 500 mg every 12 hours may be used for uncomplicated skin and skin structure infections 2
- Duration: Typically 7 days, adjusted based on clinical response 1
- Maximum daily dose: 4 grams per day; if higher doses are needed, consider parenteral cephalosporins 2
Clinical Context and Indications
Cephalexin is appropriate for methicillin-susceptible Staphylococcus aureus (MSSA) and streptococcal skin infections 1. The IDSA guidelines specifically recommend cephalexin for:
- Non-purulent cellulitis without systemic signs of infection 1
- Impetigo caused by Staphylococcus and Streptococcus species 1
- Uncomplicated skin and skin structure infections in penicillin-allergic patients (except those with immediate hypersensitivity reactions) 1
Important Caveats
Do not use cephalexin for suspected MRSA infections. If the patient has:
- Purulent drainage with systemic signs (fever, tachycardia, hypotension)
- History of MRSA colonization or infection
- Injection drug use
- Failed initial antibiotic therapy
Then empiric MRSA coverage with agents like trimethoprim-sulfamethoxazole, doxycycline, or clindamycin is required instead 1.
Dosing Alternatives
For penicillin-allergic patients without immediate hypersensitivity, cephalexin offers advantages over dicloxacillin due to:
- Availability in suspension formulation 1
- Less frequent dosing requirements compared to some alternatives 1
- Equivalent efficacy to other first-generation cephalosporins like cefazolin (when oral therapy is appropriate) 1
The 500 mg QID regimen remains the gold standard, though twice-daily dosing (500 mg BID) demonstrated equivalent efficacy in comparative trials for uncomplicated infections 3, 4, 5.
Efficacy Data
Clinical cure rates with cephalexin 500 mg QID range from 87-94% for skin and soft tissue infections caused by susceptible organisms 6, 3, 7. Microbiologic eradication rates reach 89-92% 6, 5. These outcomes are comparable to newer agents like cefdinir, though cephalexin has lower rates of diarrhea (4% vs 10%) 7, 4.