Keflex is used to treat the following infections caused by bacteria that can be killed by cefalexin: -Respiratory tract (lung and airways) infections e.g. tonsillitis, pharyngitis and bronchitis -Middle ear infection (otitis media) -Skin and soft tissue (e.g. muscle) infections -Bone and joint infections -Infections of the reproductive organs and urinary tract (e.g. cystitis), including acute inflammation of the prostate (prostatitis) -Dental infections.