Class 12 Chemistry Chemistry In Everyday Life Therapeutic Action of Different Classes of Drugs

Therapeutic Action of Different Classes of Drugs


  • The chemical substances which neutralises the excess acid in gastric juice and raise pH to an appropriate level in stomach are called antacids.
  • For example: - Baking soda, mixture of Al and Mg hydroxide are commonly used antacids.
  • Generally liquids antacids are more effective than tablets because of more of surface area available for interaction and neutralisation acids.
  • Milk is a weak antacid.
  • By using excess hydrogen carbonate stomach will become more of alkaline and as a result more of acid production happens.
  • So Metal hydroxides are used instead of them which are insoluble and don’t increase the pH value also.
  • But they will only treat the symptoms not the cause.
  • A major breakthrough in the treatment of hyperacidity happened by the discovery of chemical known as histamine which stimulates the secretion of pepsin and hydrochloric acid in the stomach.
  • 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.



  • Histamine is a potent vasodilator.
  • It has various functions. It contracts the smooth muscles in the bronchi and gut and relaxes other muscles, such as those in the walls of fine blood vessels.
  • Histamine is also responsible for the nasal congestion associated with common cold and allergic response to pollen.
  • Synthetic drugs, brompheniramine (Dimetapp) and terfenadine (Seldane) act as antihistamines.
  • They interfere with the natural action of histamine by competing with histamine for binding sites of receptor where histamine exerts its effect.
  • The antihistamines don’t affect the secretion of acid in the stomach because antiallegric and antacid drugs work on different receptors.


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