Aztreonam

• Binds peptidoglycan binding protein to inhibit the cross-linking of peptidoglycan, therefore inhibiting bacterial cell wall synthesis. 
• Because of its structure as a monobactam it is resistant to inactivation from beta-lactamases

Used in patients who are allergic to penicillin for the treatment of gram-negative rod infection. Also used for patient's who cannot tolerate aminoglycosides because of renal insufficiency. 

• gram-negative rods
  • Pseudomonas spp.
  • Klebsiella spp.
  • Serratia spp.

• GI upset

As mentioned above even though it is a beta-lactam, there are no cross allergen reactivity with penicillins.