Monobactams differ from the other beta lactam antibiotics by having a standalone beta lactam ring with a special affinity for penicillin binding protein 3, PBP3.
As a monobactam antibiotic, aztreonam is resistant to beta lactamases but may still be susceptible to extended spectrum beta lactamases.
Aztreonam has a special affinity for penicillin binding protein 3 but has a low affinity for penicillin binding protein of gram positives and anaerobes.
Like the other beta lactam antibiotics, aztreonam works by inhibiting bacterial cell wall synthesis.
Aztreonam is limited in clinical use to gram negative bacteria because of no useful activity against gram positives. Aztreonam also has no activity against anaerobes and therefore can only be used for aerobic organisms.
Aztreonam has strong activity against susceptible gram negative bacteria, especially gram negative bacilli, including organisms like Pseudomonas, Enterobacter, E. Coli, Haemophilus, Klebsiella, and Proteus.
Aztreonam is structurally different enough from penicillin that there is no cross reactivity to individuals with penicillin allergies. Therefore, this antibiotic is often used in patients who have penicillin allergies.
Many studies demonstrate synergism between aztreonam and aminoglycoside antibiotics like Gentamicin and tobramycin, especially against Pseudomonas aeruginosa.
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