Monobactams

Unlike other beta-lactams, the monobactam contains a nucleus with no fused ring attached. Thus, there is less probability of cross-sensitivity reactions.

Example:

Aztreonam (Azactam)

Mechanism Of Action:

Aztreonam is similar in action to penicillin. It inhibits mucopeptide synthesis in the bacterial cell wall. It has a very high affinity for penicillin-binding protein 3 (PBP-3) and mild affinity for PBP-1a. Aztreonam binds the penicillin-binding proteins of gram-positive and anaerobic bacteria very poorly and is largely ineffective against them.[1] Aztreonam is bactericidal but less so than some of the cephalosporins.

Indications:

Aztreonam has strong activity against susceptible gram-negative bacteria, including Pseudomonas aeruginosa. It has no useful activity against gram-positive bacteria or anaerobes. It is known to be effective against a wide range of bacteria including Citrobacter, Enterobacter, E coli, Haemophilus, Klebsiella, Proteus, and Serratia species.
Synergism between aztreonam and arbekacin or tobramycin against Pseudomonas aeruginosa has been suggested.

Administration:

Aztreonam must be administered intravenously, as the compound is poorly absorbed when given via the oral route. Phase III trials are currently in progress to measure its delivery in inhaled form, using an ultrasonic nebulizer.

Adverse effects:

Reported side-effects include injection site reactions, rash, and rarely toxic epidermal necrolysis. Gastrointestinal side effects generally include diarrhea and nausea and vomiting. There may be drug-induced eosinophilia. There is limited cross-reactivity between aztreonam and other beta-lactam antibiotics, and it is generally considered safe to admininister aztreonam to patients with hypersensitivity (allergies) to penicillins. Aztreonam is considered Pregnancy category B.