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)
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
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
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……