PHARMACOLOGY

 SYNERGISM :: 

If two or more drugs are taken simultaneously they increase the potency and /or duration of the other drug this phenomenon is called synergism Two bactericidal agents in combination produce synergistic effect e.g. streptomycin and penicillin 

Addition ::

It is a phenomenon in which the total effect of two drugs is just equal to the sum of their individual effects Combination of two bacteriostatic drugs is an example of drug addition Other example is combination of ephedrine and aminophyllin for bronchial asthma 

Antagonism ::

when the presence of one drug antagonises the action or duration of action of the other drug the phenomenon is called antagonism The total combined effect therefore is less than the algebraic total effect of the two drugs 

        Mechanism of antagonism can be of various types such as : physical chemical biochemical physiological and specific cellular antagonism 

        If adrenaline and acetylcholine are given together they neutralise each others effect Adrenaline is a vasconstrictor in action whereas acetylcholine is vasodilator So the resulting blood pressure will not be arithmetic but algebric sum Activated charcoal is as such inert but it can decrease the toxic action of alkaloidal poisons by process of adsorption Two drugs of similar action may decrease the response of each other