[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › Monobactams

[Pharmacology](https://durgical.com/en/pharmacology/) · Class

# Monobactams

β-lactams with a single ring that act only on aerobic gram-negatives and rarely cross-react with penicillin allergy; aztreonam is the only one in use.

Updated 2026-11-01

## What they are

Monobactams contain only the β-lactam ring, without the second fused ring of penicillins and cephalosporins. Aztreonam, the only member in clinical use, is an option for gram-negative infections in patients with severe allergy to other β-lactams.

## Mechanism of action

Aztreonam binds the penicillin-binding proteins of aerobic gram-negative bacteria and stops cell-wall synthesis, killing them. It has no activity against gram-positive bacteria or anaerobes. It is stable to metallo-β-lactamases but is destroyed by most ESBL and KPC enzymes.

Target: Penicillin-binding proteins of gram-negative bacteria (PBP3)

## Key points

- Only aerobic gram-negatives (including Pseudomonas): no gram-positive or anaerobic activity.
- Very little cross-allergy with other β-lactams, except possibly ceftazidime, which shares a similar side chain.
- Stable to metallo-β-lactamases, so it is combined with avibactam (or ceftazidime–avibactam) against some carbapenem-resistant gram-negatives.
- An inhaled form reduces Pseudomonas exacerbations in cystic fibrosis.

## Drugs in this class

- [**Aztreonam** An injectable or inhaled monobactam for aerobic gram-negative infections, useful in patients with severe allergy to… Penicillin-binding protein 3 of gram-negative bacteria](https://durgical.com/en/pharmacology/aztreonam/)

## Others in the class

- aztreonam–avibactam

## Test yourself

Think of the answer, then tap the question to see it.

## A patient with penicillin anaphylaxis has Pseudomonas pneumonia. Which β-lactam is usually acceptable?

Aztreonam, a monobactam with very little cross-allergy (caution only with ceftazidime allergy).

## Why does aztreonam fail against Staphylococcus aureus?

Its activity is limited to aerobic gram-negative bacteria; it has none against gram-positives or anaerobes.

## Which β-lactamases fail to destroy aztreonam?

Metallo-β-lactamases; however, ESBL and KPC enzymes do hydrolyse it.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/classes/monobactams/)

[← All of pharmacology](https://durgical.com/en/pharmacology/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 58 (McGraw Hill, 2023); [DailyMed - AZTREONAM injection, powder, lyophilized, for solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d4500795-3b07-4a7d-b432-73cafbb3dbc6) (DailyMed (U.S. National Library of Medicine), 2026); [RCSB PDB - 3PBS: Crystal structure of PBP3 complexed with aztreonam](https://www.rcsb.org/structure/3PBS) (RCSB Protein Data Bank, 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/pharmacology/classes/monobactams/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/classes/monobactams/