MONOBACTAMS AND TRIBACTAM



MONOBACTAMS
Developed in response to a desire for specific drugs aimed at gram  negative bacteria (as opposed to broad acting antibiotics).  Eg: aztreonam, tigemonam 
Aztreonam only binds to gram negative PBP. 
It has no real beta-lactam ring  and hence is  very beta-lactamase stable. 
These drugs have a very narrow spectrum and are useful only against aerobic gram negative organisms, but they can be used instead of aminoglycoside drugs (which also work against gram negative bacteria) because of their far less nephrotoxic side-effect profile
 Aztreonam: This drug is a monocyclic beta-lactam (a monobactam).  
Aztreonam interacts with penicillin binding proteins and induces the formation  of long filamentous bacteria.
Antimicrobial spectrum: The antimicrobial spectrum of aztreonam differs from that of other beta-lactams. It more closely resembles the spectrum of the aminoglycosides. Gram positive and anaerobic bacteria are resistant. Susceptible organisms include:  (It has an unusual spectrum being active only against Gram-negative aerobic rods) Enterobacteriaceae, Pseudomonas, Hemophillus and Neisseria. Aztreonam is resistant to the beta-lactamase produced by gram negative organisms.
Side effects:
Generally, the drug is well tolerated. Patients who are allergic to penicillins do not exhibit cross-reactions with aztreonam.
Toxicity is similar to that of benzyl penicillin, with no apparent cross allergy.   
These do not cause the gastrointestinal disturbances associated with carbapenems and other broad spectrum beta lactam antibiotics. 
Their inactivity against gram positive bacteria may lead to superinfection with yeasts and gram positive aerobes including Enterococcus   spp.and S.aureus
The empirical dose in animals is 30-50mg/kg,IV every 8 hours. 
It is  used in a wide variety of iinfections involving gram negative bacteria (urinary tract, lower respiratory tract, septicemia) with success as  relatively nontoxic drug in human medicine

TRIBACTAMS
They have a tricyclic structure related to that of carbapenems. 
Sanfeterinem cilexetil is the prodrug of sanfetrinem.
It has high stability to many beta lactamases and a broad spectrum of activity similar to that of carbapenems.

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