Aztreonam (trade names Azinf injection, Cayston inhalation) is a synthetic monocyclic beta-lactam antibiotic (amonobactam), with the nucleus based on a simpler monobactam isolated from Chromobacterium violaceum. It was approved by the U.S. Food and Drug Administration (FDA) in 1986. It is resistant to some beta-lactamases, but is inactivated by extended-spectrum beta-lactamases.

  • Mechanism of action
  • Spectrum of bacterial susceptibility and resistance
  • Indications and spectrum of activity
  • Administration
  • Common adverse effects
  • References
  • External links

Mechanism of action

Aztreonam is similar in action to penicillin. It inhibits mucopeptide synthesis in the bacterial cell wall, thereby blocking peptidoglycan crosslinking. It has a very high affinity for penicillin-binding protein-3 and mild affinity for penicillin-binding protein-1a. Aztreonam binds the penicillin-binding proteins of Gram-positive and anaerobic bacteria very poorly and is largely ineffective against them.[1] Aztreonam is bactericidal, but less so than some of the cephalosporins

Spectrum of bacterial susceptibility and resistance

Acinetobacter anitratus, Escherichia coli, Pseudomonas aeruginosa, and Proteus mirabilis are generally susceptible to aztreonam, while some staphylococci, Staphylococcus aureus, Staphylococcus hemolyticus and Xanthomonas maltophilia are resistant to it. Furthermore, Aeromonas hydrophila, Citrobacter diversus, Enterobacter agglomerans, Haemophilus spp. and Streptococcus pyogenes have developed resistance to aztreonam to varying degrees.

Indications and spectrum of activity

Aztreonam has strong activity against susceptible Gram-negative bacteria, including Pseudomonas aeruginosa. It has no useful activity against Gram-positive bacteria or anaerobes. It is known to be effective against a wide range of bacteria includingCitrobacter, Enterobacter, E. coli, Haemophilus, Klebsiella, Proteus, and Serratia species.[3] The following represents MIC susceptibility data for a few medically significant microorganisms.

  • Staphylococcus aureus 8 - >128 μg/ml
  • Staphylococcus epidermidis 8 - 32 μg/ml
  • Streptococcus pyogenes 8 - ≥128 μg/ml

Synergism between aztreonam and arbekacin or tobramycin against P. aeruginosa has been suggested.[5] Aztreonam is often used in patients who are penicillin allergic or who cannot tolerate aminoglycosides


Aztreonam is poorly absorbed when given orally, so it must be administered as an intravenous or intramuscular injection (trade name Azactam ), or inhaled (trade name Cayston) using an ultrasonic nebulizer. In the United States, the FDA approved the inhalation form on February 22, 2010, for the suppression of P. aeruginosa infections in patients with cystic fibrosis.[6] It received conditional approval for administration in Canada and the European Union in September 2009,[6] and has been fully approved in Australia.

Common adverse effects

Reported side effects include injection site reactions, rash, and rarely toxic epidermal necrolysis. Gastrointestinal side effects generally include diarrhea and nausea andvomiting. There may be drug-induced eosinophilia. Because of the unfused beta-lactam ring unique to aztreonam, limited cross-reactivity between aztreonam and other beta-lactam antibiotics occurs, and it is generally considered safe to administer aztreonam to patients with hypersensitivity (allergies) to penicillins.[1] Aztreonam is considered pregnancy category B.