Cephalexin is a common antibiotic that's used to treat many different bacterial infections including urinary tract infections (UTIs), ear infections, and sinus infections, to name a few. Cephalexin is a cephalosporin antibiotic that kills bacteria to fight the infection. It's safe to use in people over the age of 1, and it's typically taken by mouth 2 to 4 times per day. This medication is available as a lower-cost generic capsule, tablet, and suspension; the brand name Keflex is no longer available. Side effects can include nausea, vomiting, and diarrhea.