Tetracyclines

Tetracyclines were discovered in the 1940s and exhibited activity against a wide range of microorganisms including gram-positive and gram-negative bacteria, chlamydiae, mycoplasmas, rickettsiae, and protozoan parasites. They are inexpensive antibiotics, which have been used extensively in the prophlylaxis and therapy of human and animal infections and also at subtherapeutic levels in animal feed as growth promoters. The first tetracycline-resistant bacterium, Shigella dysenteriae, was isolated in 1953. Tetracycline resistance now occurs in an increasing number of pathogenic, opportunistic, and commensal bacteria. The presence of tetracycline-resistant pathogens limits the use of these agents in treatment of disease. Tetracycline resistance is often due to the acquisition of new genes, which code for energy-dependent efflux of tetracyclines or for a protein that protects bacterial ribosomes from the action of tetracyclines. Many of these genes are associated with mobile plasmids or transposons and can be distinguished from each other using molecular methods including DNA-DNA hybridization with oligonucleotide probes and DNA sequencing. A limited number of bacteria acquire resistance by mutations, which alter the permeability of the outer membrane porins and/or lipopolysaccharides in the outer membrane, change the regulation of innate efflux systems, or alter the 16S rRNA. New tetracycline derivatives are being examined, although their role in treatment is not clear. Changing the use of tetracyclines in human and animal health as well as in food production is needed if we are to continue to use this class of broad-spectrum antimicrobials through the present century.

The tetracyclines, 

   which were discovered in the 1940s, are a family of antibiotics that inhibit protein synthesis by preventing the attachment of aminoacyl-tRNA to the ribosomal acceptor (A) site. 

Tetracyclines are broad-spectrum agents, exhibiting activity against a wide range of gram-positive and gram-negative bacteria, atypical organisms such as chlamydiae, mycoplasmas, and rickettsiae, and protozoan parasites.

 The favorable antimicrobial properties of these agents and the absence of major adverse side effects has led to their extensive use in the therapy of human and animal infections. They are also used prophylactically for the prevention of malaria caused by mefloquine-resistant Plasmodium falciparum. 

Furthermore, in some countries, including the United States, tetracyclines are added at subtherapeutic levels to animal feeds to act as growth promoters. Although the tetracyclines retain important roles in both human and veterinary medicine, the emergence of microbial resistance has limited their effectiveness. 

Undoubtedly the use of tetracyclines in clinical practice has been responsible for the selection of resistant organisms. Nevertheless, as we enter the new millennium, the use of tetracyclines and other antibiotics as animal growth promoters is becoming increasingly controversial because of concerns that this practice may be contributing to the emergence of resistance in human pathogens. 

The increasing incidence of bacterial resistance to tetracyclines has in turn resulted in efforts to establish the mechanisms by which genetic determinants of resistance are transferred between bacteria and the molecular basis of the resistance mechanisms themselves. 

The improved understanding of tetracycline resistance mechanisms achieved by this work has provided opportunities for the recent discovery of a new generation of tetracyclines, the glycylcyclines. Further research, already under way, is also identifying approaches by which inhibitors of tetracycline resistance mechanisms might be developed for use in conjunction with earlier tetracyclines to restore their antimicrobial activity .

The tetracyclines have been extensively reviewed both by the present authors and others . Nevertheless, in view of continuing interest in this group of antibiotics for both infectious and noninfectious diseases , we have decided to write a review that focuses on recent developments in the field.

What drugs are in the tetracycline class?

• Doxycycline^#
• Chlortetracycline.
• Clomocycline.
• Demeclocycline.
• Lymecycline.
• Meclocycline.
• Metacycline.
• Minocycline.

 What is a tetracycline antibiotic agent?

Tetracycline is a broad spectrum polyketide antibiotic produced by the Streptomyces genus of Actinobacteria. It exerts a bacteriostatic effect on bacteria by binding reversible to the bacterial 30S ribosomal subunit and blocking incoming aminoacyl tRNA from binding to the ribosome acceptor site.

What are the side effects of tetracycline?

• sores or swelling in your rectal or genital area;
• mild nausea, vomiting, diarrhea, or stomach upset;
• white patches or sores inside your mouth or on your lips;
• swollen tongue, trouble swallowing; or.
• vaginal itching or discharge.