Interaction of Drugs

02Sep08

1. Synergistic Interaction
   1. Pharmacological phenomenon of drug interaction when the drugs increase action of each other.
   2. 2 main types
      1. 1+1=2 : Drug which administrated, all increase the effect of each other and some of its effect is sum up.
      2. 1+1>2 : Drug which enhances/amplifies the effect of each other, usually drugs of CNS
2. Antagonism
   1. Pharmacological phenomenon of drug interaction when the drugs decrease action of each other
   2. Types:
      1. Chemical antagonism
         1. Chemical neutralization of drug
         2. Formation of insoluble chemical non-active complexes (chelations)
      1. Pharmacokinetic antagonism
         1. Changes in absorption of other drug
         2. Changes in biotransformation of other drug
            1. Increase/activates
            2. Decrease/inhibits
         1. Changes in distribution/redistribution
            1. After injection/administration of drugs, it enters the blood to be transported
            2. Some drugs bind to certain structure of transporters (protein plasma, tissue etc)
            3. Some drugs change the distribution of another drug
         1. Changes in excretion
            1. Some drugs change the output of others
      1. Pharmacodynamic / physiological antagonism
         1. Competitive – both drugs act on one target site of the receptor
         2. Non-competitive – drugs act on different target site but produce opposite effect to each other
         3. Allosteric – drug acts on allosteric centres.

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