This document discusses the principles of pharmacodynamics, which is the study of how drugs act on the body. It explains that drugs can stimulate or depress the activity of specialized cells through various mechanisms, including interacting with enzymes, ion channels, transporters, and receptors. The key actions of drugs are stimulation, depression, irritation, replacement, and cytotoxic effects. Most drugs produce their pharmacological responses by interacting with target biomolecules like proteins. Common examples of drug mechanisms discussed are captopril inhibiting the angiotensin converting enzyme, quinidine blocking myocardial sodium channels, and amphetamines inhibiting dopamine reuptake.

1. PHARMACODYNAMICS

2. PHARMACOLOGY
Pharmacology is the science of drugs .
Drug: “ A drug is any chemical molecule, which can be administered exogenously
into the living system produce biological response or effect.”
PHARMACOLOGY
PHARMACOKINETICS
Kinesis meaning movement
- What the body does to the drug
PHARMACODYNAMICS
Dynamics meaning action / power
- What the drug does to the body

3. Pharmacodynamics is the study of drug effects.
• It describes, what the drugs do and how they do.
“what the drug does to the body when they enter”
• Drugs (except those gene based) do not impart new functions to any
system, organ or cell; they only alter the pace of ongoing activity.
Example : Adrenaline reacts with adrenoreceptors and ultimately leads to
cardiac stimulations .
PHARMACODYNAMICS

4. PRINCIPLES OF DRUG ACTION
Stimulation
Depression
Irritation
Replacement
Cytotoxic action

5. STIMULATION
DEPRESSION
Enhancement of the levels of activity of specializes cells . Eg : Adrenaline
stimulates heart . However , excessive stimulation is often followed by
depression of that function .
Eg : Picrotoxin , a CNS stimulant , produces convulsions followed by coma and
respiratory depression on high doses .
Selective diminution of activity of specialized cells .
Eg : barbiturates depress CNS , quinidine depress heart . Some drugs stimulate
one type of cells but depress the other
Eg: Ach ( acetylcholine ) stimualtes intestinal smooth muscles but depress SA
node in heart .

6. IRRITATION
REPLACEMENT
Non selective and noxious effect
Eg : counterirritant such as heat or an ointment increases blood flow to the
site , but strong irritants can cause inflammation and even necrosis .
Use of natural metabolites , hormones in deficiency state .
Eg : levodopa in Parkinsons , insulin in diabetes and iron in anemia .
Selective cytotoxic action for invading parasite or cancer cells , attenvating them
without significantly affecting the host cells .
Eg : penicillin , chloroquine , zidovudine , cyclophosphamide
CYTOTOXIC ACTION

7. MECHANISM OF DRUG ACTION
● ENZYMES
● ION CHANNELS
● TRANSPORTERS
● RECEPTORS
● A drug can bring about physical or chemical change in cell environment .
eg : stool softners ( MgOH ) that act by altering surface tension .
● Majority of drug produce their effects by
interacting with target biomolecules.
ie.proteins

8. ENZYMES
• Enzymes are protein molecules that
accelerates chemical reactions .
• Almost all biological reactions are carried out
by enzymes.
• Drugs can either increase or decrease the
rate of enzymatically mediated reactions.
Eg : captopril inhibits ACE ( angiotensin
converting enzyme )

9. IONS CHANNELS
● There are many ion channels in our
body which helps transmembrane
signaling and regulate intracellular
ionic composition .
● Eg ; Na , K channel , Ca channel
● Drugs can affect ion channels .
● Drugs can also affect ion movement
by directly binding on channel .
● Eg : quinidine blocks myocardial Na+
channel .

10. TRANSPORTERS
● Several substrates are move across
membrane by binding to specific
transporter .
● Many drugs affect this , they interact
with carrier and inhibit the movement of
metabolite/ ion .
Eg : amphetamines selectively block
dopamine reuptake in brain neurons by
dopamine transporters .

11. RECEPTORS
● Receptors are proteins or binding sites
which present on surface and inside the
cells , drugs bind with it , activate it and
give its pharmacological response .
 AGONIST – an agent which activate
receptors to produce effects .
Eg : opioids
 ANTAGONIST – an agent which inhibit
the action of agonist .
Eg : naloxone

12. THANK YOU !!