- lac·tam 'lak-.tam n any of a class of amides of amino carboxylic acids that are formed by the loss of a molecule of water from the amino and carboxyl groups, that are characterized by the carbonyl-imido group -CONH- in a ring, and that include many antibiotics compare LACTIM, LACTONE
* * *lac·tam (lakґtəm) a cyclic amide formed from aminocarboxylic acids by the elimination of water. They are isomeric with lactims, which are enol forms of lactams.
Medical dictionary. 2011.