Drugs » Antibiotics

Antibiotics

Introduction

An antibiotic is a chemical substance that inhibits or abolishes the growth of micro-organisms, such as bacteria, fungi and protozoa. The term originally referred to any agent with biological activity against living organisms; however, "antibiotic" now is used to refer to substances with anti-bacterial, anti-fungal, or anti-parasitical activity. The first antibiotic compounds used in modern medicine were produced and isolated from living organisms, such as the penicillin class produced by fungi in the genus Penicillium, or streptomycin from bacteria of the genus Streptomyces. With advances in organic chemistry many antibiotics are now also obtained by chemical synthesis, such as the sulpha drugs. Majority of antibiotics are obtained from fungi but some like bacitracin, colistin, polymyxin b are obtained from bacteria. Some antibiotics are now entirely synthesized by chemical methods e.g. Chloramphenicol.

The organisms susceptible to the inhibitory or lethal effect of an antibiotic constitute its 'spectrum'. According to their spectra, antibiotics may be classified as:

1. Antibiotics mainly effective against Gram +ve bacteria
   1. Systemic infections e.g. Penicillin, Erythromycin, Lincomycin, Vancomycin, Fucidin.
   2. Topical infections e.g. Bacitracin.
2. Antibiotics mainly effective against Gram -ve bacteria
   1. Systemic infections e.g. Streptomycin, Kanamycin, Gentamicin, Amikacin, Colistin, Polymyxin B and Cycloserine.
   2. Local in the intestine e.g. Paromomycin.
3. Antibiotics effective against both Gram-Positive and Gram-Negative Bacteria
   1. Systemic infections e.g. Ampicillins, Amoxycillins, Carbenicillins, Cephalosporins, Rifamycins.
   2. Topical infections e.g. Neomycin, Framycetin
4. Antibiotics effective against both Gram-Positive and Gram-Negative Bacteria, Rickettsia and Chlamydia
   Tetracyclines and Chloramphenicol.
5. Antibiotics effective against Acid Fast Bacilli (M. tuberculosis)
   Streptomycin, Rifampicin, Cycloserine, Capreomycin and Kanamycin.
6. Antibiotics effective against Protozoa
   Tetracycline, Paromomycin.
7. Antibiotics effective against fungi
   Nystatin, Amphotericin-B, Griseofulvin.
8. Antimalignancy antibiotics
   Actinomycin D, Mitomycin and Azaserine.