Cephalexin is a semisynthetic first-generation cephalosporin antibiotic having methyl and beta-(2R)-2-amino-2-phenylacetamido groups at the 3- and 7- of the cephem skeleton, respectively. It is effective against both Gram-negative and Gram-positive organisms, and is used for treatment of infections of the skin, respiratory tract and urinary tract. It has a role as an antibacterial drug. It is a cephalosporin, a semisynthetic derivative and a beta-lactam antibiotic allergen. It is a conjugate acid of a cephalexin(1-).