Cephalexin Dosing for MSSA Infections

Adult Dosing

The Infectious Diseases Society of America recommends cephalexin dosing at 500 mg orally every 6 hours for more severe infections or less susceptible organisms in adults, with treatment duration of 7-14 days for most skin and soft tissue infections 1
For uncomplicated skin infections, the treatment duration is 7 days 2
For surgical site infections, cephalexin should be dosed at 500 mg orally every 6 hours 1

Cephalexin should only be used for confirmed or suspected MSSA infections, as it has no activity against MRSA 3
Cultures should be obtained before starting therapy when possible to confirm methicillin susceptibility 3
For pyomyositis caused by MSSA, cefazolin or antistaphylococcal penicillin is recommended, with cephalexin as an oral step-down option 1
MRSA infections should be treated with trimethoprim-sulfamethoxazole, clindamycin, or vancomycin instead of cephalexin 3
Severe infections with systemic toxicity should be started with IV therapy before considering oral step-down 1
Necrotizing fasciitis or gas gangrene requires broad-spectrum IV therapy, not oral cephalexin 1

Patients should be reassessed at 48-72 hours, and if no improvement is seen, cultures should be obtained, and alternative antibiotics or broader coverage for MRSA should be considered 3, 4
It should not be assumed that all staphylococcal infections are methicillin-susceptible without obtaining cultures, especially in areas with high MRSA prevalence 3