Antibiotics

Antibiotic Medicines

Originally, natural products secreted by microorganisms (microbes) that inhibit the growth of other microorganisms. The term is now commonly used, however, to denote any drug, natural or synthetic, that has a selective toxic action on bacteria, protozoans, or other single-celled microorganisms.

Antibiotics are not active against viruses. The more accurate term is therefore antimicrobials. While many are now produced synthetically, they are still based on the natural compounds. Antibiotics used to treat bacterial infections are called antibacterial drugs.

Antibacterials may kill bacteria, in which case they are described as bactericidal , or they may prevent bacterial growth, when they are referred to as bacteriostatic. They are usually designed to exploit some aspect of bacterial structure that is not present in mammalian cells and therefore they do not harm human cells. For example, penicillins and cephalosporins (collectively known as beta-lactam antibiotics) attack bacterial cell walls; mammalian cells do not have cell walls.

Aminoglycosides and tetracyclines attack bacterial ribosomes (the protein-synthesizing machinery of the cell), which are different from mammalian ribosomes. Antibiotics that are active against a wide variety of microorganisms are known as broad-spectrum antibiotics; those effective only against particular microbes are called narrow-spectrum antibiotics.

Widespread use of antibiotics results in bacteria developing resistance to these agents. Antibiotics are therefore, in most Western countries, prescription only medicines. The normal healthy human body contains several types of bacteria and other microbes, notably in the gut. Use of antibiotics can have a harmful effect on some of these microbes, which results in the overgrowth of others causing superinfections , which may present more problems than the original infection.