Imipenem is a broad spectrum b-lactam antibiotic which is related to the penicillin/cephalosporin family of antibiotics. Imipenem works by interfering with the ability of bacteria to form cell walls, and therefore the bacteria break up and die. Imipenem, the active antibiotic ingedient, is partially inactivated by an enzyme in the kidney which can reduce its effectiveness. Therefore it is combined with cilastatin which blocks the effect of this enzyme. Cilastatin does not have any antibacterial effects and does not affect the antibacterial activity of the imipenem.