Cephalexin treats bacterial infections by inhibiting bacterial cell wall synthesis. It belongs to the cephalosporin class of antibiotics and is effective primarily against gram-positive bacteria like Streptococcus and Staphylococcus species. Cephalexin binds to penicillin-binding proteins within the bacterial cell wall, preventing the final stages of peptidoglycan synthesis, which is crucial for cell wall strength and rigidity. This disruption leads to cell lysis and death.

Because of its mechanism, cephalexin is effective in treating skin infections, respiratory tract infections, urinary tract infections, and bone infections. It is usually taken orally, well-absorbed, and generally safe with a good side effect profile.