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1. [PHARMACOVIGILANCE (Mechanism Of Drug Action & Factors
Modifying Drug Action)] December 15, 2014
Pristyn Research PVT LTD | Confidential
PHARMACOVIGILANCE (MECHANISM OF DRUG ACTION & FACTORS
MODIFYING DRUG ACTION)
Learning Objectives:
 To understand Drug Action
 Various Types of Drug Action
 Mechanism of Drug Action
 Which Factors Modifies drug action
Description:
As we stated that Pharmacovigilance is the science and activities relating to the detection, assessment,
understanding and prevention of adverse effects, but prior to understanding of adverse effects one should
know the various actions produced by Drug. As a drug after administration into the body elicit various
physiological and biochemical changes inside the body; and produce its desire effect. Various mechanisms
are responsible for the action of drug. A brief discussion of the mechanism of drug action and various
factors modifying drug action and dosage is covered in this chapter of Pristyn Research.
Drug Action:
Drug Action means the interaction between drug and blood or drug and tissue cells result in modification of
existing function.
Types of Drug Action:
1) Stimulation 2) Depression 3) Irritation 4) Replacement 5) Physical Action 6) Chemical Reaction
1) Stimulation:
Stimulation indicates an increase in the activity of specialized cells.
Example: Caffeine stimulates cerebral cortex

2. [PHARMACOVIGILANCE (Mechanism Of Drug Action & Factors
Modifying Drug Action)] December 15, 2014
Pristyn Research PVT LTD | Confidential
2) Depression:
This is the term used to indicate decrease in the normal activity of specialized cells.
Example: Barbiturates depress the central nervous system.
3) Irritation:
Irritation indicates the injurious effect of drug on growth nutrition and morphology of non-specialized
cells capable of producing inflammation.
Example: Irritant Purgative like senna.
4) Replacement:
The term replacement is used to indicate the use of glandular secretions namely hormones obtained
from animal in the treatment of deficiency diseases in human beings.
Example: Insulin is commonly used in the treatment of diabetes.
5) Physical Action:
Some drug act in pure mechanical way because of their physical properties
Example: Saline purgative for osmotic pressure
6) Chemical Reaction:
Some drug act because of their chemical properties, or by chemical combination with substance present
in the body.
Example: Antacids neutralize gastric acidity due to their chemical interaction with acids from gut.

3. [PHARMACOVIGILANCE (Mechanism Of Drug Action & Factors
Modifying Drug Action)] December 15, 2014
Pristyn Research PVT LTD | Confidential
Mechanism of Drug Action:
It is believed that most of the drugs produce their effects by combining with enzymes, cell membranes or
other specialized functional components of the cell. The drug cell interaction is supposed to alter the
function of the cell component thereby initiating a series of biochemical & physiological changes that a
drug is liable to produce inside the body. This type of action is also produced by Drug receptors.
Drug receptors:
The receptor mechanism explains drug action and is believed to be one of the known mechanisms of action
of drug. No other mechanism of action could satisfactorily explain the drug action. But, this involves a
series of very complex physiological and biochemical process which are explained in the figure 1 and
attached video below.
Figure: 1. Drug Receptor Mechanism
Factors Modifying drug action: (Detail Explained in attached video)
Body weight Age Route of administration Additive effect Synergism Antagonism Drug Tolerance
Practice Questions:
1) Explain in the detail Drug-Receptor mechanism.
2) What is Affinity, intrinsic activity & partial antagonist?
3) How generic factor modifies drug action? Explain with example.
4) State concept of Tachyphylaxis.
5) Give account on each type of Drug Tolerance.