ureidopenicillin ureidopenicillin the ureidopenicillins are a group of penicillins which are active against pseudomonas aeruginosa. azlocillin piperacillin mezlocillin there are three ureidopenicillins in clinical use: azlocillin piperacillin mezlocillin they are mostly ampicillin derivatives in which the amino acid side chain has been converted to a variety of cyclic ureas. it is speculated that the added side chain mimics a longer segment of the peptidoglycan chain, more than ampicillin, and thus would bind more easily to the penicillin-binding proteins. ureidopenicillins are not resistant to beta-lactamases. they are used parenterally, and are particularly indicated in infections caused by gram-negative bacteria.