Macrolides

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The macrolides are a large group of antibacterials mainly derived from Streptomyces spp. and having a common macrocyclic lactone ring to which one or more sugars are attached. They are all weak bases and only slightly soluble in water. Their properties are very similar and in general they have low toxicity and a similar spectrum of antimicrobial activity with cross-resistance between individual members of the group.

The macrolides are bacteriostatic or bactericidal, depending on the concentration and the type of micro-organism, and are thought to interfere with bacterial protein synthesis. They reversibly bind to the 50S ribosomal subunit of the 70S ribosome of sensitive microorganisms, thereby inhibiting the translocation step of protein synthesis, wherein a newly synthesized peptidyl tRNA molecule moves from the acceptor site on the ribosome to the peptidyl (donor) site, and consequently inhibiting RNA-dependent protein synthesis leading to cell growth inhibition and cell death.

 

Aminoglycosides: An Overview

Aminiglycosides are bactericidal and active against some Gram-positive and many Gram-negative organisms. They are not absorbed from the gut (although there is a risk of absorption in inflammatory bowel disease and liver failure) and must therefore be given by injection for systemic infections.

Following active transport into the cell, they bind irreversibly to a specific aminoglycoside receptor on the bacterial 30S ribosomal subunit and interfere with the initiation complex between messenger RNA and the 30S subunit, thereby inhibiting initiation of protein synthesis, consequently leading to bacterial cell death. In addition, they induce misreading of the mRNA template causing incorrect amino acids to be incorporated into the growing polypeptide chain, consequently interfering with protein elongation.