Monobactams

Agent: aztreonam

Aztreonam is the only monobactam available.  Structurally, aztreonam contains only the four-membered ring of the basic beta-lactam structure,  hence the name monobactam. Aztreonam’s quirk is that it seems to be safe to administer to patients with allergies to other beta-lactams, except patients who have a specific allergy to ceftazidime.  This cross-reactivity seems to be a result of the fact that ceftazidime and aztreonam share an identical side chain. Ceftazidime and aztreonam also share virtually the same spectrum of activity. It is reason-ably safe to remember the utility of aztreonam by thinking of it as ceftazidime without allergic cross-reactivity with other beta-lactams.

Spectrum

Good: Pseudomonas, most GNRs

Moderate: Acinetobacter

Poor : Gram-positive organisms, anaerobes

Adverse Effects

Similar to those of other beta-lactams, but with a low incidence of hypersensitivity.

Important Facts

• Aztreonam shares a mechanism of action and pharmacodynamic profile with other beta-lactams. Because it is a Gram-negative drug that is often used in patients with penicillin allergies,  it is often confused with aminoglycosides. It is chemically unrelated to aminoglycosides and does not share their toxicities.

• Aztreonam can be administered via inhalation to patients with cystic fibrosis to prevent exacerbations of infection.

• Aztreonam is a type of beta-lactam, and combination therapy with it and other beta-lactams against the same organism is unwarranted. Try adding a non-beta-lactam drug to your empiric regimen for serious nosocomial infections instead.

What It’s Good For

Gram-negative infections, including Pseudomonas, particularly in patients with a history of beta-lactam allergy.

Don’t Forget!

Before using aztreonam in your patients with beta-lactam allergies, investigate whether the reaction was specifically to ceftazidime. If you cannot deter-mine this and the reaction was serious, proceed with caution or use an alternative agent.

References

Gallagher ,J.C. and MacDougall ,c. (2012). Antibiotics Simplified. Second Edition. Jones & Bartlett Learning, LLC.

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