|Trade names||Azactam, Cayston, others|
|Intravenous, intramuscular, inhalation|
|Defined daily dose||0.2 gram (inhalation)|
4 gram (by injection)
|Bioavailability||100% (IM) 0.1% (by mouth in rats) Unknown (by mouth in humans)|
|Metabolism||Liver (minor %)|
|Elimination half-life||1.7 hours|
|Chemical and physical data|
|Molar mass||435.43 g·mol−1|
|3D model (JSmol)|
|Melting point||227 °C (441 °F) (dec.)|
Aztreonam, sold under the brand name Azactam among others, is an antibiotic used primarily to treat infections caused by gram-negative bacteria such as Pseudomonas aeruginosa. This may include bone infections, endometritis, intra abdominal infections, pneumonia, urinary tract infections, and sepsis. It is given by injection into a vein or muscle or breathed in as a mist.
Common side effects when given by injection include pain at the site of injection, vomiting, and rash. Common side effects when inhaled include wheezing, cough, and vomiting. Serious side effects include Clostridium difficile infection and allergic reactions including anaphylaxis. Those who are allergic to other β-lactam have a low rate of allergy to aztreonam. Use in pregnancy appears to be safe. It is in the monobactam family of medications. Aztreonam usually results in bacterial death through blocking their ability to make a cell wall.
Aztreonam was approved for medical use in the United States in 1986. It was removed from the World Health Organization's List of Essential Medicines in 2019. It is available as a generic medication. In the UK the injectable form costs the NHS about £28 per day while the inhaled form costs about £2,182 for a course of treatment. It is a manufactured version of a chemical from the bacterium Chromobacterium violaceum.
Nebulized forms of aztreonam are used to treat infections that are complications of cystic fibrosis and are approved for such use in Europe and the US; they are also used off-label for non-CF bronchiectasis, ventilator-associated pneumonia, chronic obstructive pulmonary disease, mycobacterial disease, and to treat infections in people who have received lung transplants.
Spectrum of activity
Escherichia coli, Pseudomonas aeruginosa, and Proteus mirabilis are generally susceptible to aztreonam, while some bacteria have resistance toward it. Furthermore, Enterobacter cloacae, Serratia marcescens, Citrobacter freundii have developed resistance to aztreonam to varying degrees.Aztreonam is often used in people who are penicillin allergic or who cannot tolerate aminoglycosides.
It has no useful activity against Gram-positive bacteria or anaerobes. It is known to be effective against a wide range of bacteria including Citrobacter, Enterobacter, E. coli, Haemophilus, Klebsiella, Proteus, and Serratia species. 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
Aztreonam is poorly absorbed when given by mouth, so it must be administered parenterally (as an intravenous or intramuscular injection, or inhaled using an ultrasonic nebulizer). In the United States, it was approved for inhalation in 2010, for the suppression of P. aeruginosa infections in people with cystic fibrosis. It received conditional approval for administration in Canada and the European Union in 2009, and has been fully approved in Australia.
Reported side effects include injection site reactions, rash, and rarely toxic epidermal necrolysis. Gastrointestinal side effects generally include diarrhea and nausea and vomiting. There may be drug-induced eosinophilia. Because of the unfused beta-lactam ring unique to aztreonam, there is somewhat lower cross-reactivity between aztreonam and many other beta-lactam antibiotics, and it may be safe to administer aztreonam to many patients with hypersensitivity (allergies) to penicillins and nearly all cephalosporins. However, like other beta lactams, there is a risk of serious allergic reactions, including anaphylaxis. This is more likely if the patient is allergic to a certain cephalosporin known as ceftazidime. Aztreonam exhibits cross-reactivity with this cephalosporin due to a similar side chain. 
Special caution is warranted in patients who are allergic to ceftazidime and are subsequently placed on aztreonam therapy.
Mechanism of action
Aztreonam is similar in action to penicillin. It inhibits synthesis of the bacterial cell wall, by 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.
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