1

A PRESENTATION ON

DRUG ANTAGONISM

Presented by-

Vipul Agarwal

BBAU, Lucknow

DRUG ANTAGONISM

One drug or inhibits action of another drug

i.e

Effect of A + B < Effect of drug A + Effect of drug B

Types of Antagonism

a) Physical antagonismb) Chemical antagonismc) Physiological/functional

antagonismd) Pharmacological antagonism

A) Physical Antagonism

Based on physical property of drugs, e.g. charcoal (adsorb alkaloid) in alkaloidal poisoning

B) Chemical Antagonism

A type of antagonism where a drug counters the effect of another by simple chemical reaction / neutralization(not binding to the receptor)

e.g. Calcium sodium edetate form insoluble complexes with arsenic / lead

C) Functional Antagonism (Physiological Antagonism)

Opposite effects of two drugs on same function

Two drugs act on two diff. types of receptors & antagonize action of each other

e.g. Glucagon and insulin on blood sugar level

D) Pharmacological Antagonism

Competitive Non-competitive

Equilibrium Non-equilibrium (Reversible) (Irreversible)

Antagonist Receptor

Antagonist-Receptor

ComplexDENIED!

Competitive Antagonism

1.Same receptor by forming Weak bonds

2.Maximal response is concentration dependent

3.The effect of antagonist can be overcome by increasing the concentration of agonist

4. Parallel rightward shift of DRC

COMPETITIVE Reversible ANTAGONISM

Cont……

e.g. Atropine and Acetylcholine at Muscarinic -R Naloxone and Morphine at opioid-R

COMPETITIVE Irreversible ANTAGONISM

1. Have affinity for the same receptor sites and bind in an irreversible manner by covalent bond

2. Effects cannot be overcome even by increasing the concentration of the agonist

3. LDR curves of agonist would show reduced efficacy but altered potency

e.g. Dibenamine and NE at α1 adrenoceptors

Agonist Receptor

Antagonist

‘Inhibited’-ReceptorDENIED!

NON COMPETITIVE ANTAGONISM

i. Binds to site other than the agonist site

ii. Prevent the receptor activation by the agonist

e.g. Flumazenil by binding to BZD site antagonises the effects of BZD by preventing the binding of GABA to GABAA receptor

Cont……

Cont……

REFERENCES

Sharma – Priciples of Pharmacology,

2nd Edition K.D Tripathi – Essentials of Medical

Pharmacology, 7th edition R.S Satoskar – Pharmacology and

Pharmacotherapeutics, 18th Edition www.google.com