2. Content
Introduction
Types of drug action effect (Type of responses)
Mechanism of Drug Action
Receptor Families Four types of receptors families
Special Type of receptors
Antagonism
3. Introduction
Pharmacodynamics is a Greek word, Pharmacon means Drug and
Dynamics means Action/Power.
It covers all the aspects relating to “What a drug does to the body”
Mechanism of action.
Action: How and Where the effect is produced is called as Action.
Effect: The type of response producing by drug.
Pharmacodynamics Study of the biochemical and physiological effects of
drugs on the
⁕ Body
⁕ Microorganisms
⁕ Parasites within or on the body and
⁕ Mechanisms of drug action and the relationship between drug
concentration and effect
4. TYPES OF DRUG ACTION
EFFECT (Type of responses):
Stimulation it is selective enhancement of the level of activity of
specialized cells. E.g. adrenaline stimulate the heart.
Inhibition/Depression it is selective diminution of activity of
specialized cells. E.g. quinidine depresses heart.
Replacement This refers to the use of natural metabolites, hormones in
deficiency states. E.g. iron in anaemia.
Irritation This refers a nonselective, often noxious effect and is
particularly applied to less specialized cells. Eg: counterirritants
increase blood flow to the site.
Cytotoxic action For invading parasites or cancer cells. Eg:penicillin
5. Mechanism of Drug Action
A drug may produce its effects through various mechanism
Physical action:
Osmosis
Drug retains water by osmosis as osmotic diuretics (Mannitol) and
osmotic purgatives (Lactulose).
Adsorption
Drug adsorbs diverse substances including toxins and fluid on its surface
thereby inactivating them (activated charcoal).
6. Chemical action:
Antacids neutralize gastric acidity (e.g. NaHCO3)
Chelating agents form biologically inactive complex with other
substances.
Regulatory Proteins (Body Control systems):
Enzymes
Drugs may inhibit or activate certain enzymes. -Carrier Molecules:
Drugs may increase their synthesis or block their recognition site.
7. Molecules
Drugs may increase their synthesis or block their recognition site.
Ion Channels
Drugs may open ion channels by acting on specific receptor which
forms the channel or drugs may physically close the channel
Receptors
Responses to drug-receptor interaction can be as Agonist (substance
binds and activates the receptor) or Antagonist (substance blocks the
receptor).
Receptors are macromolecules
Most are proteins
Present either on the cell surface, cytoplasm or in the receptor
8. Drug(D) +Receptor® Drug receptor complex Response
Drug receptor interaction:1. Selectivity:- Degree of complimentary co
relation between drug and receptor. Ex:- Adrenaline Selectivity for α,
ß Receptor
Affinity:- Ability of drug to get bound to the receptor.
Intrinsic activity (IA) or Efficacy:- Ability of drug to produce a
pharmacological response after making the drug receptor complex.
Response
9.
10. Receptor Families
Four types of receptors families
1. Receptors with intrinsic ion channels.
2. G- protein coupled receptor
3. Enzymatic receptors
4. intracellular receptor
Receptors with intrinsic ion channels
⁕ located on the cell surface
⁕ They enclose ion selective channels for Na, K, Ca, Cl.
⁕ When an agonist is bound to these receptors they convey signals.
11. G- protein coupled receptor
located on the cell membrane
G protein is a connecting link between receptor and effector systems,
like enzymes, carrier molecules etc.
They are called so because of their link with GDP AND GTP
Intracellular receptor
Present either in cytoplasm or nucleus of the cell.
Vitamin A ,corticosteroids etc. act through these receptors.
Enzymatic receptors
These are enzyme molecules themselves Eg: tyrosine protein kinase.
12. SPECIAL TYPE OF RECEPTORS
SPARE RECEPTORS
SILENT RECEPTORS
PRESYNAPTIC RECEPTORS
THERAPEUTIC INDEX(TI)
It is a measure of the relative safety of a drug for a particular treatment.
Therapeutic index = LD50 / ED50
Large value - a wide margin of safety. Eg. Penicillin
Small value - a narrow margin of safety Eg: warfarin
13. ANTAGONISM
When one drug decreases or abolishes the action of another. Effect of
drug A+ B < Effect of drug A+ Effect of drug B Types :
Physical antagonism
Chemical antagonist.
Physiological antagonist.
Pharmacological antagonist
14. Competitive Antagonist
The antagonist dissociates rapidly from the receptor.
The antagonist effect can be overcome by increasing the agonist
concentration. e.g. morphine & naloxone
Non-competitive Antagonist
The antagonist dissociates very slowly or not at all from the receptor
The action of antagonist cannot be overcome by increasing the
agonist concentration .
