Chemistry Therapeutic Action of Different Classes of Drugs : I
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### Topics Covered :

● Therapeutic Action of Different Classes of Drugs
● Antacids
● Antihistamines

### Therapeutic Action of Different Classes of Drugs :

Therapeutic action of a few important classes of drugs is given below :

### Antacids :

=> Over production of acid in the stomach causes irritation and pain.

=> In severe cases, ulcers are developed in the stomach.

=> Until 1970, only treatment for acidity was administration of antacids, such as sodium hydrogen carbonate or a mixture of aluminium and magnesium hydroxide.

=> However, excessive hydrogen carbonate can make the stomach alkaline and trigger the production of even more acid.

=> Metal hydroxides are better alternatives because of being insoluble, these do not increase the color{red}(pH) above neutrality.

=> These treatments control only symptoms, and not the cause.

=> Therefore, with these metal salts, the patients cannot be treated easily.

=> In advanced stages, ulcers become life threatening and its only treatment is removal of the affected part of the stomach.

### Antihistamines

=> In hyper acidity, a chemical histamine 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.

color{red}("Note ") : Antihistamines do not affect the secretion of acid in stomach because antiallergic and antacid drugs work on different receptors.