Monobactams

Question 1

What is the mechanism of action of aztreonam (monobactam)?

Answer 1

Aztreonam binds specifically to penicillin-binding protein 3 (PBP3) of Gram-negative bacteria, inhibiting peptidoglycan cross-linking and causing cell lysis. It is bactericidal.

Question 2

Describe the spectrum of activity of aztreonam.

Answer 2

Aztreonam is effective only against aerobic Gram-negative bacteria, including Enterobacteriaceae and Pseudomonas aeruginosa. It has no activity against Gram-positive organisms or anaerobes.

Question 3

How does aztreonam’s beta-lactam structure influence cross-reactivity and resistance?

Answer 3

Aztreonam has minimal cross-allergenicity with other beta-lactams and is resistant to many beta-lactamases produced by Gram-negatives. Resistance can occur via certain beta-lactamases or PBP3 mutations.

Question 4

Outline key pharmacokinetic features of aztreonam.

Answer 4

Aztreonam is given IV or IM, distributes well including into CSF, and is primarily excreted unchanged in the urine. It has a short half-life (~1.5-2 hours) requiring frequent dosing.

Question 5

What are the clinical indications for aztreonam?

Answer 5

Aztreonam is used for serious Gram-negative infections, especially in patients allergic to penicillins/cephalosporins or those with renal insufficiency. Examples include pneumonia, sepsis, UTIs, and intra-abdominal infections.

Question 6

What are the adverse effects of aztreonam?

Answer 6

Aztreonam is generally well tolerated. Possible effects include injection site reactions, rash, mild transaminase elevations, and GI upset. Cross-allergy is very rare.

Question 7

Why is aztreonam safe to use in penicillin-allergic patients?

Answer 7

Aztreonam’s structure is sufficiently different from penicillins and cephalosporins, so it typically does not trigger allergic reactions in those patients.

Question 8

Is there a mnemonic for aztreonam’s use or spectrum?

Answer 8

“Aztreonam is Aztremely (extremely) specific for Aerobic Gram-negative Rods.” Remember Aztreonam for Aerobic gram-negatives and for Allergic (penicillin-allergic) patients.

Question 9

What is the mechanism of action of vancomycin (monobactam)?

Answer 9

Binds the precursors of D-ala-D-ala and inhibits bacterial cell wall growth.

Question 10

Describe the spectrum of activity of vancomycin.

Answer 10

• Gram positive coverage including MRSA.
• C. diff

Question 11

What are the major adverse reactions caused by vancomycin?

Answer 11

• Nephrotoxicity.
• Ototoxicity (rare).
• Infusion reactions (diffuse flushing) that can be ameliorated with antihistamines and a rate of infusion that is slower.