Pharmacodynamics

1. Pharmacodynamics
Presented
by
Ferdows Ahmed
Roll:570
Batch: 19th
Semester: 5th
Department of Pharmacy

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

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 .