What is the clinical use of aztreonam and its advantage in penicillin-allergic patients?

• A. Treat Gram-negative infections including Pseudomonas; safe in penicillin allergy.
• B. Treat MRSA infections; not safe in penicillin allergy.
• C. Broad-spectrum including anaerobes; significant cross-reactivity with penicillin.
• D. Used mainly for Gram-positive cocci; contraindicated in penicillin allergy.

Answer: (A)

Aztreonam is a monobactam antibiotic that is highly active against Gram-negative bacteria, including Pseudomonas aeruginosa, making it a good choice for serious Gram-negative infections when a beta-lactam is needed but penicillin cannot be used. Its advantage in penicillin-allergic patients comes from its minimal cross-reactivity with penicillins, since its structure differs from penicillins and most cephalosporins, so it can be safely given to many patients with penicillin allergies. It does not cover MRSA or anaerobes and is not effective against Gram-positive organisms, so its use is limited to Gram-negative infections.