Jagadeeswaran Appusamy

CYCLOSERINE Broad spectrum antibiotic, also effective against many bacteria including Mycobacterium. Being an analog of D-alanine inhibits bacterial cell wall formation by preventing d-ala-d-ala dipeptide synthesis required for formation of NAMA pentapetide (Peptidoglycon).  TYROTHRICIN It is a mixture of Gramocidin and Tyrocidine , obtained from B. brevis, mainly active against G +ve org., including Strepto. and Staphylo. It acts on cell membrane and causes leakage and also uncouples oxidative phosphorylation in bac. The drug is not absorbed orally, is too toxic for systemic use and causes hemolysis. Used in bovine mastitis during dry period as intramammary infusion, to treat metritis and topically for skin and ear infections. It does not cause hypersensitivity reactions.   NOVOBIOCIN Obtained biosynthetically from   2 actinomycetes viz., Streptomyces niveus and S.spheroides. It is narrow spectrum antibiotic, mainly bacteriostatic and cidal at h

Polymyxins Polymyxin B & E (Colistin) are two clinically important polypeptide antibiotics obtained from Bacillus polymyxa and Bacillus colistinus respectively. Both are narrow spectrum, rapidly bactericidal antibiotics. Highly active against G -ve orgs. Such as E. Coli, Salmonella spp. And P. Aeruginosa. They are ineffective against G +ve orgs. These have detergent like action on the Bac.’s cell membrane. They bind with bac. Cell membrane phospholipids with high affinity, distort it. As a result ions, aminoacids, etc leak out and bac. Cells die. They are neither absorbed topically nor orally and do not penetrate BBB. For systemic they are administered parenterally. Systemically rarely used due to serious toxicity (nephrotoxicity, neurotoxicity and neuromuscular blockade) and only used in life threatening infections caused by G –ve bacilli or Pseudomonas. Orally it is used in G – ve enteritis in calves and pigs, topically in skin infections (along with neo

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