Monobactam
![Aztreonam. (The four-membered ring at the bottom is the β-lactam. There is a second thiazole ring, but it is not fused to the β-lactam ring.)](/Images/godic/202501/28/Aztreonam_structure.svg4730.png")
![Tigemonam](/Images/godic/202501/28/Tigemonam4730.png")
Monobactams are β-lactam compounds wherein the β-lactam ring is alone and not fused to another ring, in contrast to most other β-lactams. They are effective only against aerobic Gram-negative bacteria (e.g., Neisseria, Pseudomonas).
The only commercially available monobactam antibiotic is aztreonam.