In this article we will discuss about:- 1. Structure of Tetracylines 2. Antibiotic Spectrum of Tetracylines 3. Mechanism of Action.
Structure of Tetracylines:
All members of the group of tetracyclines consist of a common four-ring structure to which a variety of side chains (R1, R2, R3) are attached (Fig. 45.14).
Antibiotic Spectrum of Tetracylines:
Tetracyclines are broad-spectrum bacteriostatic antibiotics active against gram- negative and gram-positive bacteria, rickettsias, chlamydias, and mycoplasmas. Due to their close similarity in chemical nature, cross resistance of pathogens to them is common, i.e., a pathogen developing resistance to any one of them may show resistance to rest of them.
Tetracyclines, in general, show low toxicity, quick absorbility, and quick excretability. Therefore these are very suitable antibiotics, but with a serious drawback which is that they destroy the natural intestinal flora and, as a result, an undesirable development of resistant staphylococci and yeasts (e.g., Candida) may gain upper-hand.
High doses of tetracyclines may cause side effects such as nausea, diarrhoea, yellowing of teeth in children, and damage to the liver and kidneys.
Mechanism of Action of Tetracylines:
Tetracyclines inhibit protein synthesis. The mechanism of their action is by combining with the 30S subunit of bacterial ribosome and inhibiting the binding of aminoacyl tRNA molecules to the aminocyl site (A site) of ribosome (Fig. 45.15).
