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)
Drugs in this class
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.
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 (DailyMed (U.S. National Library of Medicine), 2026); RCSB PDB - 3PBS: Crystal structure of PBP3 complexed with aztreonam (RCSB Protein Data Bank, 2026).
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Representative model, for educational purposes only.