Drug interaction: chemical and dispositional antagonism.pptx

Drug antagonism occurs when two or more drugs interact and one or more of their effects are reduced or blocked. This happens when the drugs have opposite effects on the body.
Drug antagonism can be caused by four main mechanisms: chemical, pharmacokinetic, receptor, and physiological.
Antagonism can be reversible or irreversible, and competitive or non-competitive. Antagonists themselves have no effect on a receptor and are said to have neither intrinsic activity nor efficacy.
Some examples of drug antagonism include: Acetylcholine-cinchonidine and Antagonism of pyridylethylamine and antihistamines.
pA is a scale that can be used to measure the effectiveness of an antagonist and some of its characteristics.

1. Chemical & Dispositional Antagonism Dr Dimithri Devraj

2. Antagonism When one drug decreases or abolishes the action of another drug

3. Types Of Antagonism functional dispositional chemical Receptor

4. Chemical Antagonism Also called inactivation Chemical reaction between 2 compounds that produce a less toxic product Examples – Chelators of metal ions decrease toxicity Antitoxins antgonize action of animal toxins

5. Chelators Also called chelants They form coordination bond with the metal ions Example - Ca-Na-EDTA forms insoluble complex with arsenic / lead Dimercaprol chelates heavy metals (Pb,As,Hg)

6. ADDING CHELATOR HEAVY METAL

7. Dispositional Antagonism Absorption , biotransformation, distribution, or excretion of a chemical is altered Concentration & duration of the chemical at the target organ decreases

8. Application Prevention of absorption of a toxicant (by charcol or ipecac) Increase activity of metabolizing enzyme with enzyme inducers Increase excretion of chemical(by diuresis) Reduce toxicity

9. Examples Ammonium chloride / ascorbic acid decreases amphet toxicity Tetracyclin + oral contraceptive 🡪 failure of contraceptive Rifampin + doxycyclin 🡪 loss of efficacy of doxycycline Allopurinol + warfarin 🡪 inhibit metabolism

10. Tetracyclin + Oral Contraceptive TETRACYCLIN ORAL CONTRACEPTIVE Anti biotic Inhibits protein synthesis by blocking attachment of charged aminoacyl-tRNA to A site of ribosome Contains estrogen and a progestin INTERACTION Interruption of enterohepatic circulation Contraceptive failure occur RIFAMPIN has similar action by increasing metabolism of steroids