chemistry 12th class cbse notes

Therapeutic Action of Different Classes of Drugs


These are the drugs used to reduce or abolish pain without causing the loss of consciousness, paralysis and some other disturbances. For example- Asprin, Analgin, Paracetamol.

Analgesics are of two types:

  • Narcotics: These drugs relieve pain but also produce sleep or drowsiness. These are habit forming drugs and are also termed as addictive drugs.
    For example: Morphine, codeine, heroin.
  • Non-narcotics: These are non-habit-forming drugs also named as non-addictive drugs. These are used to reduce mild to moderate pains such as headache, toothache, muscle and joint pain, etc. These drugs do not produce drowsiness.
    For example: Asprin, paracitamol.


Tranquillizers are the chemicals used to relieve stress, mental tension, anxiety. These form a major component of the sleeping pills. Most of these drugs are derivatives of barbituric acid. Examples: Luminal, Equanil, iproniazid, barbiturate.



Tranquillizers are of two types:

  • Sedative: Reduce nervous tension and promote relaxation.
    e.g. Reserpine, barbituric acid and its derivatives as luminal & seconal.
  • Mood elevators or Antidepressants: A drug used for treatment of highly depressed patient, who has lost his confidence.
    e.g. Benzedrine (amphetamine)


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.

Antiseptics and Disinfectants:

Antiseptics and disinfectants are also the chemicals which either kill or prevent the growth of microorganisms.


  • Which prevent or destroy the growth of the harmful microorganism, common antiseptics are – Dettol, Savlon, Cetavelon, acriflavin, iodine, methylene blue, mercurochrome & KMnO4.
  • Dettol is a mixture of chloroxylenol and terpineol. Its dilute solution is used to clean wounds.
  • Bithional – It is added to soap to impart antiseptic properties



The chemical compounds capable of completely destroying the microorganism are termed as disinfectants. These are toxic to living tissues. These are utilized for sterilization of floor, toilets instruments & cloths.
eg: 1% solution of phenol is disinfectant while 0.2% solution of phenol is antiseptic.


The chemical substances produced from some microorganism (fungi, bacteria or mold) and are used to inhibit the growth of another microorganism.

These are effective in the treatment of infections diseases. e.g. Penicillin – It is highly effective drug for pneumonia, Bronchitis, abcesses, sore throat etc.

  • Synthetic antibiotics are Streptomycin – (Tuberculosis),
  • Chloromycetin – (Typhoid, Meningitis, Pneumonia, diarrhoea, dysentary etc.)
  • Tetracyclins – (Acute fever, trachoma, dysentery & urinary tract infection).

Antifertility Drugs:

Antibiotic revolution has provided long and healthy life to people. The life expectancy has almost doubled. The increased population has caused many social problems in terms of food resources, environmental issues, employment, etc.

Norethindrone is an example of synthetic progesterone derivative most widely used as an antifertility drug.

The estrogen derivative which is used in combination with progesterone derivative is ethynylestradiol (novestrol)

Antifertility Drugs


Also known as the anti-allergic drug, it suppresses the action of histamine (a compound released by cells in response to injury or any allergic and inflammatory reactions).

The drug cimetidine (Tegamet), was designed to prevent the interaction of histamine with the receptors present in the stomach wall. This resulted in release of lesser amount of acid. The importance of the drug was so much that it remained the largest selling drug in the world until another drug, ranitidine (Zantac), was discovered.


For example: Terfinadine, Cimetidine.

Synthetic drugs, brompheniramine (Dimetapp) and terfenadine (Seldane), act as antihistamines.



The chemical substances which neutralize the excess acid in stomach and give relief from acidity are called antacids.

For example: Sodium hydrogencarbonate (NaHCO3), magnesium hydroxide [Mg(OH)2] and aluminium hydroxide [Al(OH)3].


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