A carbapenam is the parent member of the ò-lactams compounds. The parent is of only of theoretical interest, but substituted derivatives are important carbapenem antibiotics, originally inspired by the structure of penicillin. In penicillin, the five-membered ring contains sulfur, whereas carbapenams have a CH<sub>2</sub> in place of S. A related class of antibiotics are unsaturated carbapenems. Carbapenam-based antibiotics are widely used, but resistant strains of some pathogens have emerged.