PHARMACOLOGY

 DRUG -ANTAGONISM ::

It is a type of drug interaction in which the effect of one drug is reduced or inhibited in the presence of another drug The mechanism is explained on the basis of drug receptor interactions As mentioned before it is believed that when a drug is added to a biological system it is bound to a complementary stereospecific area on the effector cell membrance termed as receptor The degree of association of drug with receptor is defined as affinity and the property to produce a response is known as intrinsic activity Certain drugs possess both affinity as well as intrinsic activity such drugs are described as agonists However certain drugs possess only affinity but have no intrinsic activity such drugs are not capable of producing any effect of its own but prevent the effect of the agonist Such drugs are referred to as antagonists 

    There are two types of antagonism : 1.Competitive 2.Non -competitive 

Competitive Antagonism ::

If the antagonist binds reversibly to the receptor and its inhibitory effect is overcome by increasing the dose of the agonist such an inhibition is referred to as competitive antagonism 

    In such cases it is possible to obtain the maximum response of agonist Graphically it is represented by (1) rightward parallel shift of dose response curve (2) surmountable maximum response (3) no change in the slope of the curve 

Some examples of competitive antagonism ::

1.Acetylcholine and Atropine 

2.Noradrenaline and Phentolamine 

3.Isoprenaline and Propranolol 

4.Histamine and Mepyramine