A monobactam antibiotic for Gram-negative infections, useful in penicillin allergy
Aztreonam
An antibiotic used for Gram-negative infections, often useful when someone is allergic to penicillin.
What is Aztreonam?
Aztreonam is an antibiotic from the monobactam group, used mainly for infections caused by Gram-negative bacteria, including Pseudomonas. It is given into a vein in hospital, and there is also an inhaled form used for lung infection in cystic fibrosis. A particular advantage is that it usually does not cross-react with penicillin allergy, so it can often be used safely in people who are penicillin-allergic, though caution is needed with the cephalosporin ceftazidime because of a shared side-chain. Like other antibiotics, it can occasionally lead to C. difficile diarrhoea.
Education and reference only. This is a plain-language guide to Aztreonam — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Aztreonam is an antibiotic belonging to a small group called the monobactams. It is effective specifically against Gram-negative bacteria, a category that includes organisms such as Pseudomonas, but it does not cover Gram-positive bacteria or anaerobes. It is usually given into a vein in hospital, and an inhaled form is used to treat ongoing lung infection in people with cystic fibrosis. It is particularly valued as an option for people who are allergic to penicillin, because it rarely triggers the same allergy.
How it works
Aztreonam kills Gram-negative bacteria by interfering with the building of their cell wall, the protective outer layer they need to survive. Because of its particular structure, it targets Gram-negative bacteria specifically and leaves Gram-positive and anaerobic bacteria largely unaffected. Its chemical structure is different enough from penicillins that the immune system usually does not confuse the two, which is why it can often be used in people with penicillin allergy. However, it shares part of its structure (a side-chain) with the cephalosporin ceftazidime, so caution is needed in people allergic to that medicine.
Company & origin
Originated / developed by: Specialist manufacturers.
A monobactam antibiotic used in UK hospitals for infections caused by Gram-negative bacteria, and as an inhaled form for the lungs in cystic fibrosis; valued because it is usually safe in penicillin allergy.
Practical use
How to take Aztreonam
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- The injection is given into a vein by a hospital team; the inhaled form is breathed in as your specialist has shown you.
- Tell the team about any allergies, especially to the antibiotic ceftazidime, before it is given.
- If you use the inhaled form, follow advice about using a bronchodilator first to reduce coughing or wheezing.
- Complete the full course as prescribed, even if you feel better, to clear the infection.
- Tell the team if you develop diarrhoea, especially if it is severe or persistent.
Weighing it up
Advantages & disadvantages of Aztreonam
Advantages
- Usually safe to use in people allergic to penicillin, as it rarely cross-reacts.
- Effective specifically against Gram-negative bacteria, including Pseudomonas.
- Available as an inhaled form for ongoing lung infection in cystic fibrosis.
Disadvantages
- Covers only Gram-negative bacteria, so often needs combining with another antibiotic.
- Used with caution in people allergic to the cephalosporin ceftazidime because of a shared side-chain.
- Like other antibiotics, can cause diarrhoea, including C. difficile infection.
Practical use
Good to know
The standout feature of aztreonam is that it usually does not cross-react with penicillin allergy, making it a valuable option for treating Gram-negative infections in people who cannot take penicillins. There is one important exception: it shares a side-chain with the cephalosporin ceftazidime, so it is used with caution in anyone allergic to ceftazidime. It covers Gram-negative bacteria only, so it is often combined with another antibiotic when Gram-positive or anaerobic bacteria might also be involved. Like all antibiotics, it can disturb the gut and occasionally cause C. difficile diarrhoea, so any troublesome diarrhoea should be reported. The inhaled form, used in cystic fibrosis, can sometimes cause coughing or wheezing, so a bronchodilator is often used beforehand. It is given and monitored by a specialist team.
Who should not take it / use with caution
- People who have had a serious allergic reaction to aztreonam should not receive it.
- It is used with caution in people allergic to ceftazidime, because the two share part of their chemical structure.
- It is used with care, with dose review, in people with kidney problems and in pregnancy, under specialist guidance.
Monitoring
- Reviewing the response to treatment and the specific bacteria involved.
- Checking kidney function so the dose can be adjusted if needed.
- Watching for allergic reactions, diarrhoea, and, with the inhaled form, breathing symptoms.
Side effects
- Stomach upset, nausea or diarrhoea, including, less commonly, C. difficile infection.
- Rash or, less often, allergic-type reactions.
- With the inhaled form, coughing, wheezing or throat irritation; sometimes changes in liver blood tests.
Key interactions
- It is often combined deliberately with other antibiotics to broaden cover, guided by the team.
- Tell the team about all your medicines, as with any antibiotic, so interactions can be reviewed.
- Other medicines that affect the kidneys may matter when doses are adjusted for kidney function.
Available as: A powder made up for injection or infusion into a vein, and an inhaled (nebulised) form for the lungs.
Answers
Aztreonam: frequently asked questions
What is aztreonam used for?
It is an antibiotic for infections caused by Gram-negative bacteria, including Pseudomonas, given into a vein, with an inhaled form used for lung infection in cystic fibrosis.
Can I have it if I am allergic to penicillin?
Usually yes. Aztreonam rarely cross-reacts with penicillin allergy, which is one reason it is valued, but always tell the team about your allergies.
Why is ceftazidime allergy a concern?
Aztreonam shares part of its chemical structure (a side-chain) with the cephalosporin ceftazidime, so it is used with caution in people allergic to ceftazidime.
Does it cover all bacteria?
No. It covers only Gram-negative bacteria, so it is often combined with another antibiotic when Gram-positive or anaerobic bacteria may also be involved.
Can it cause diarrhoea?
Yes, like other antibiotics it can cause diarrhoea, including, less commonly, a gut infection called C. difficile; report any severe or persistent diarrhoea.
Authoritative sources
- BNF
- NICE CKS
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