The ureidopenicillins are a group of penicillins which are active against Pseudomonas aeruginosa.^{[citation needed]}

There are three ureidopenicillins in clinical use:^[1]

• 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.^{[citation needed]}

They are used parenterally, and are particularly indicated in infections caused by Gram-negative bacteria.^{[citation needed]}