- Diseases in human beings and animals may be caused by a variety of microorganisms such as bacteria, virus, fungi and other pathogens.
- An antimicrobial tends to destroy/prevent development or inhibit the pathogenic action of microbes such as bacteria (antibacterial drugs), fungi (antifungal agents), virus (antiviral agents), or other parasites (antiparasitic drugs) selectively.
- Antibiotics, antiseptics and disinfectants are antimicrobial drugs.
- Antibiotics are used as drugs to treat infections because of their low toxicity for humans and animals.
- An antibiotic is a substance produced wholly or partly by chemical synthesis, which in low concentrations inhibits the growth or destroys microorganisms by intervening in their metabolic processes.
- In order to find chemicals this will affect the invading bacteria and not the host.
- Paul Ehrlich, a German bacteriologist, conceived this idea. He investigated arsenic based structures in order to produce less toxic substances for the treatment of syphilis.
- He developed the medicine, arsphenamine, known as salvarsan.
- Although salvarsan is toxic to human beings, its effect on the bacteria, spirochete, which causes syphilis, is much greater than on human beings.
- He noted that there is similarity in structures of salvarsan and azodyes. The –As = As– linkage present in arsphenamine resembles the –N = N – linkage present in azodyes in the sense that arsenic atom is present in place of nitrogen.
- In 1932, he succeeded in preparing the first effective antibacterial agent, prontosil, which resembles in structure to the compound, salvarsan. Soon it was discovered that in the body prontosil is converted to a compound called sulphanilamide, which is the real active compound. Thus the sulpha drugs were discovered.
- A large range of sulphonamide analogues was synthesised. One of the most effective is sulphapyridine.
- Despite the success of sulphonamides, the real revolution in antibacterial therapy began with the discovery of Alexander Fleming in 1929, of the antibacterial properties of a Penicillium fungus.
- Antibiotics have either cidal (killing) effect or a static (inhibitory) effect on microbes.
- A few examples of the two types of antibiotics are as follows:
- Antibiotics which kill or inhibit a wide range of Gram-positive and Gram-negative bacteria are said to be broad spectrum antibiotics.
- Those are effective mainly against Gram-positive or Gram-negative bacteria are narrow spectrum antibiotics.
- If effective against a single organism or disease, they are referred to as limited spectrum antibiotics.
- Penicillin G has a narrow spectrum. Ampicillin and Amoxicillin are synthetic modifications of penicillin’s. These have broad spectrum.
- It is absolutely essential to test the patients for sensitivity (allergy) to penicillin before it is administered.
- In India, penicillin is manufactured at the Hindustan Antibiotics in Pimpri and in private sector industry.
- Chloramphenicol, isolated in 1947, is a broad spectrum antibiotic.
- It is rapidly absorbed from the gastrointestinal tract and hence can be given orally in case of typhoid, dysentery, and acute fever, certain form of urinary infections, meningitis and pneumonia.
- Vancomycin and ofloxacin are the other important broad spectrum antibiotics.
- The antibiotic dysidazirine is supposed to be toxic towards certain strains of cancer cells.