PHARMACOLOGY

 MODE OF ACTION OF DRUGS ::

A drug can act by virtue of its various properties like physical chemical physiological etc Examples of the action of drugs by virtue of these properties are as follows :: 

PHYSICAL PROPERTIES ::

(A) Taste : Certain compounds have a bitter taste and by virtue of this they reflexly increase the flow of hydrochloric acid in the stomach and improve the appetite e.g. quassia chirata etc 

(B) Physical mass :: Here a drug may not have any intrinsic action but by its mechanical action it produces the effect e.g. taking isapgol orally increases the bulk in the intestine so as to produce laxative effect 

(C) Osmosis :; Certain substances as such are inert but by virtue of their osmosis draw out water and produce the necessary action for example osmotic diurectics like mannitol and purgative like magnesium sulfate 

(D) Absorption :: Kaolin particles absorb water on its surface and thereby reduce gut motility This action is useful to control diarrhoea 

(E) Soothing effect :: By soothing the surface irritation can be prevented which may be useful in the treatment of cough (e.g.syrups) eczema (e.g.calamine lotion )etc 

(F) Electrolytic action :: Drugs in solution can undergo partial disintegration into electrically charged particles called ions Some bear a positive charge and are called cations while others bearing a negative charge are known as anions Thus when a drug exhibibits an ionic action it may be anionic or cationic An antianaemic drug like ferrous carbonate or ferrous sulphate owes its action to the ferrous cation (+) and not to its action (-) sulphate or carbonate which are inert whereas in the case of sodium sulphate or sodium tartarate it is the anion (-) sulphate or tartarate which decides the purgative action and not the cation (+) sodium here the action is anionic such anionic action is influenced by the extent of its ionization and its activity is affected by temperature pH enzyme action and substrate concentration 

(G) Radioactivity :: The radioactive substances (like 131 I) are commonly used in treatment of cancer