The document provides an overview of pharmacodynamics, which examines the actions of drugs on the body and their mechanisms of action, categorizing drug effects into stimulation, depression, irritation, replacement, cytotoxic actions, and immune modification. It discusses receptor-mediated and non-receptor mediated mechanisms, including the role of receptors, enzyme actions, and the impact of factors such as dose response and drug interactions. Additionally, it highlights the significance of therapeutic index and the combined effects of drugs, including synergism and antagonism.

1. PHARMACODYNAMICS
Dr. Ab.Siddique.P.A
Associate Professor
Pharmacology & Therapeutics
Dr. sid
Associate Professor
Pharmacology

2. Introduction
• Study of actions of the drugs on the body &
their mechanisms of action
• Drugs produce their effects by interacting
with physiological systems of organisms
• Drugs only modify rate of functions of various
systems; they cannot change the basic
functions of any physiological system

3. PHARMACODYNAMICS
• What the drug does to the body.
• Study of drug effects. How? And What?
• Pharmacodynamics deals with the study of
biochemical and physiological effects of
drugs and their mechanisms of action.

4. Dose
Absorption
Distribution
Metabolism Pharmacokinetics
Excretion
Drug in the plasma
Drug at the site of action
Pharmacodynamics
MOA & Effect- Adverse and Beneficial

5. PRINCIPLES [Types] OF DRUG ACTION
1. Stimulation
– Adrenaline
– Pilocarpine
2. Depression
– Quinidine
– Morphine
– Barbiturates
3. Irritation
– Bitters
– Counter irritants
4. Replacement
• Insulin
• Iron
• Levodopa
5. Cytotoxic action
•Penicillin,
•Chloroquine
• cyclophosphamide
6. Modification of
immune status
•Vaccines
•Sera

6. Mechanism of Drug Action
Non-receptor mediated Receptor mediated
•Physical
•Chemical
•Enzymes
•Antibody
•Placebo
•Receptors on
the cell
membrane
•Receptors
inside the
cell

7. Mechanisms of drug action
Physical action:
• Physical property of the drug
is responsible
– E.g. mass: bulk laxatives
– Adsorptive : charcoal
– Osmotic activity: magnesium sulfate
– Radioactivity: radioactive iodine
– Radioopacity: barium sulfate

8. Mechanisms of drug action
Chemical action:
• Extracellular chemical interactions
–E.g. antacids neutralize gastric HCl
–Chelating agents used in poisoning
treatment

9. Mechanisms of drug action
Through enzymes:
• Stimulation: unusual
• Relevant to endogenous mediators
• E.g. adrenaline stimulates adenyl
cyclase

10. Mechanisms of drug action
• Enzyme inhibition:
–Non specific inhibition:
• Certain chemicals alter the tertiary
structure of any enzyme with which
they come in contact E.g. alcohol,
formaldehyde

11. Enzyme inhibition
–Specific inhibition:
• Competitive: Overcome by
increasing substrate conc.
– E.g. physostigmine &
neostigmine compete with
acetyl choline for
cholinesterase
• Non competitive: inhibitor
reacts with adjacent site &
not with catalytic site,
alters enzyme such that it
loses its catalytic activity
– E.g. aspirin & cyclooxygenase

12. Mechanism of Drug Action - Non-receptor
Mediated
Antibody production Examples
• Stimulation of
AB production
in body
• BCG against TB,
Polio vaccine
against Polio

13. Mechanism of Drug Action - Non-receptor
Mediated-Placebo effect
• Placebo: Dummy medicine without
Pharmacological effect
• Uses:
1. Relief of subjective symptoms- Eg .Anxiety
2. In Clinical trials to reduce bias
• Factors affecting
1. Pt factors-With neurotic symptoms
2. Drug factor-Injection, Capsules
3. Doctor factor-Personality, Fame, Dr - Pt
relationship

14. Mechanism of Drug Action - Receptor
Mediated
• Receptor:
 Protein macromolecules
 Present on cell wall or
 Inside the cell
 To which drug binds, interacts and
produces action
• Drug[D]+Receptor[R]↔D-R-Complex→Action
Eg. Adrenergic, Muscarinic

15. Drug
Receptor
Effect
RECEPTOR MEDIATED DRUG ACTION
D-R
Binding
Second messengers

16. Receptor Super Families
MEMBRANE BOUND RECEPTORS
• GPCR: Eg. Muscarinic, Adrenergic
receptors
• Ligand gated Ion channel: Eg. Nicotinic
receptors
• Enzymatic: Eg. Insulin receptor
 INTRACELLULAR RECEPTORS
• Nuclear Receptors: Eg. Steroid, Thyroid
hormone

17. endocrine and the sensory systems.
References:
G-Protein coupled[GPCR]
Ligand gated ion channels
Nuclear receptors
Enzymatic receptors
Receptor Super Families

19. Receptor Regulation
Downregulation Upregulation
• Prolonged use of agonists
[Salbutamol]
↓
Receptor no. and sensitivity
[β2 receptors] ↓ ↓
↓
Drug effect ↓ ↓
[Decreased effect on chronic
use]
• Prolonged use of
antagonists
[Propranolol]
↓
Receptor no. and sensitivity
[β2 receptors] ↑↑
↓
[Sudden withdrawal →
Increased sensitivity of
adrenoreceptors→ Angina

20. Receptor Mediated- Terms
Affinity: Ability of the drug to bind to
receptor
Intrinsic activity: Ability of drug to produce
pharmacological activity after binding

21. • Substance that binds & produces a
response similar to the physiological
signal molecule
Agonist
• Substance that binds to receptor &
prevents the action of agonist, but no
effect of its own
Antagonist
• Binds to receptor but has low intrinsic
activity, i.e. produces partial response
Partial agonist
Inverse agonist
•Activates receptor & produces a
response in the opposite direction to
that of agonist
Receptor mediated drug action

22. Dose response relationship
• Potency of drug: Amount of the drug required
to produce a response
– E.g 1 mg of bumetanide produces same diuresis as
50 mg of frusemide
– Less clinical significance
• Efficacy :
– Indicates maximum response that can be produced
by a drug
– E.g. Frusemide produces powerful diuresis which
cannot be produced by any dose of amiloride
– Great clinical significance

23. Dose response
• Dose-Response relationship: Relationship
between Pharmacological effect and dose
[Concn.of drug at site of action]
• Graded or quantitative: As the dose
administered in a single sub or tissue is
increased, response increases in a graded
fashion
Graded
• Quantal or all or none: frequency with
which any drug evokes a all or none
response in a population
Quantal

24. Therapeutic window phenomenon
• Optimal therapeutic effect exerted
only over a narrow range of plasma drug
conc.or drug doses; both below & above
this range, beneficial effects are
suboptimal
• E.g. Tricyclic antidepressants, Clonidine,
glipizide

25. Therapeutic index
Therapeutic index = median lethal dose
median effective dose
• Indicates safety margin of drug
• Drugs with low therapeutic index have
low safety margin
• E.g. digoxin, lithium

27. 100→
50% →
50% →
0 →
ED50 LD50
TI Narrow TI WIDE
TI=10/5=2 TI=100/5=20

28. Combined effect of drugs
• When 2 drugs are administered together:-
1. They may be Indifferent to each other
2. One may increase the action of the
other- Synergism
3. Action may be decreased or abolished
Antagonism

29. Combined effect of drugs
Indifferent Synergism Antagonism
One facilitates
the action of
other
One opposes the
action of other
Additive
Supra-additive
[Potentiation]
Competitive
Non-
competitive
Physical
Chemical
Physiological
Receptor

30. Combined effect of drugs
Synergism : (Greek: Syn-together,
ergon-work)
• Action of one drug is facilitated or
increased by the other
• Additive: effect of drugs A + B = effect
of drug A + effect of drug B
– E.g. aspirin + paracetamol =
analgesic/antipyretic

31. Synergism
Supra additive: (potentiation)
• Effect is greater than individual
effects of components
• Effect of drug A+ B=> effect of drug A
+ effect of drug B
• E.g. acetyl choline + physostigmine
(inhibition of break down)
– Levodopa + carbidopa (inhibition of
peripheral metabolism)

32. Antagonism
• Drug decreases or inhibits the action of
another
• Effect of drug A + B< effect of drug A
+ effect of drug B
• Usually one drug is inactive as such;
decreases the effect of another

33. Physical antagonism
• Based on physical property of the drugs
• E.g. charcoal adsorbs alkaloids & can
prevent absorption
Chemical Antagonism:
Drugs react chemically & form inactive
product
e.g. KMnO4 oxidizes alkaloids: used for
gastric lavage in poisoning

34. In vitro chemical antagonism
• Drugs might react when mixed in same
syringe or infusion bottle
• E.g. thiopentone sodium + succinyl
choline
• Penicillin + succinyl choline
• Heparin + penicillin/
tetracycline/streptomycin

35. Physiological/ functional antagonism
• Two drugs act on different receptors or
by different mechanisms, but have
opposite effects on the same
physiological function
• Pharmacological effects in opposite
direction
• E.g. Histamine & adrenaline on bronchial
muscles & BP

36. Receptor mediated antagonism
• Antagonist interferes with the binding
of agonist with its receptor or inhibits
generation of response as a result of
binding
• Competitive & non-competitive
• E.g. acetyl choline & atropine
– Morphine & naloxone
– Diazepam & bicculline

37. Competitive[Surmountable] Noncompetitive[Unsurmountable]
1. Binds with the same site
on the receptor
2. Resembles the agonist
3. Surmountable by
incresing the concn. Of
agonist
4. Rightward shift of DRC
5. Eg.
Ach – atropine
Morphine - Naloxone
1. Binds to another site or
same site covalently
2. No resemblance
3. Not surmountable
4. Flattening of DRC
5. Eg.
Diazepam –Bicuculline
Phenoxybenzamine-
Noradrenaline
Antagonism