Pharmaceutical worker holding a bottle of cephalexin. Cefalexin is used to treat a number of bacterial infections, including: middle ear infections, strep throat, bone and joint infections, pneumonia, skin infections, and urinary tract infections. It may be used to prevent bacterial endocarditis. It is ineffective against methicillin-resistant Staphylococcus aureus. It may be used in those who have mild or moderate allergies to penicillin, but is not recommended is those with severe allergies. It has no effect against viral infections.