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.