what is the antibiotic cephalexin
1 Cephalexin, also known by the brand names KeflexÂ® and RilexineÂ®, is an antibiotic used for dogs and cats. 2  Cephalexin belongs to the cephalosporin class of drugs and iis related to the penicillin drugs in how it kills bacteria. cephalosporins have a much broader range of activity against bacteria than penicillins.