This document discusses pharmacodynamics, which is the study of how drugs act on the body and their mechanisms of action. It covers key pharmacodynamic principles like drug targets, mechanisms of drug action, dose-response relationships, and factors that influence therapeutic effectiveness. The main drug targets discussed are enzymes, ion channels, transporters, and receptors. The mechanisms of drug-receptor interactions like agonism, antagonism, and partial agonism are also summarized.

1. Pharmacodynamics
For BPH 1st Year
Dr. Pravin Prasad
2nd Year Resident, MD Clinical Pharmacology
Maharajgunj Medical Campus, Institute of Medicine
22nd December, 2016 (Poush 7, 2073), Thursday

2. Introduction
“Pharmacodynamics is the study of the
biochemical and physiological effects of drugs and
their mechanisms of action”
- Bluementhal DK, Garrison JC. Pharmacodynamics: Molecular Mechanisms of Drug Action. In:
Bruton LL, Chabner BA, Knollmann BC, editors. Goodman & Gilman’s The Pharmacological Basis of
Therapeutics. 12th ed. China: Mc Graw Hill Education; 2011. p 41-72
Pharmacodynamics is the study of drug effects
• What & How

3. Introduction
Action-Effect
sequence
Dose-Effect
relationship
Pharmacodynamics
Modification of
action of one drug
by another drug

4. Principles of Drug Action
Stimulation:
• Selective enhancement of the
level of activity of specialized
cells
Replacement:
• Use of natural metabolites, hormones, or their congeners in
deficiency states
Irritation:
• Non-selective, often noxious
effect on less specialized cells
Depression:
• Selective diminution of the level
of activity of specialized cells
Cytotoxic Action:
• Selective cytotoxic action on
invading microbes or cancer
cells

5. • Physical interaction
• Chemical interaction
• Binding to proteins
• Binding to Nucleic acids
• Drug Targets
• Receptors
• Ion channels
• Carriers (transporters)
• Enzymes
Mechanism of Drug Action
RICE

6. Drug Target- Enzymes
• Enzyme stimulation
• Pyridoxine 
decarboxylase
• Enzyme inhibition
• Competitive (equilibrium
type)
• Competitive (non-
equilibrium type)
• Non-competitive
Non-competitive

7. Drug Target- Enzymes
Enzyme Endogenous
substrate
Inhibitor Type
Bacterial folate
synthase
Para-amino
benzoic acid
Sulfadiazine
Competitive
(equilibrium)
Cholinesterase Acetylcholine Physostigmine
Malathion, OPs Competitive
(non-
equilibrium)
Dihydrofolate
reductase
DHF Methotrexate

8. Drug Target- Enzymes
Enzyme Endogenous
substrate
Inhibitor Type
Carbonic
anhydrase
H2O and CO2 Acetazolamide
Non-
competitive
H+-K+ ATPase H+ and K+ Omeprazole
Cyclooxygenas
e
Arachidonic
acid
Aspirin

9. Drug Targets- Ion Channels
•Types:
•Ligand gated
• Nicotinic receptors
•G-protein regulated channels
• β1 adrenergic receptor activated Ca++ channels
•Voltage operated
• Local anaesthetics, phenytoin, Nifedipine
•Stretch sensitive

10. Drug Targets- Ion Channels

11. Drug Targets- Transporters (Carriers)

12. Drug Targets- Transporters (Carriers)
Carrier Transports Blockers
Norepinephrine
transporters
Noradrenaline
(Norepinephrine)
Desipramine,
Cocaine
Gamma butyric acid
transporter (GAT1)
GABA Tiagabine
Na+ - K+ - 2Cl- co-
transporter
Na+, K+, Cl- Furosemide
Serotonin
Transporter
Serotonin Fluoxetine

13. Pharmacodynamics
For BPH 1st Year
Dr. Pravin Prasad
2nd Year Resident, MD Clinical Pharmacology
Maharajgunj Medical Campus, Institute of Medicine
9th February, 2017 (Magh 27, 2073), Thursday

14. Drug Targets- Receptors
• Are the macromolecule or binding site located on the surface or
inside the effector cell that serves to recognise the signal
molecule/drug and initiate a response to it, but itself has no other
function
-Tripathi KD. Pharmacodynamics: Mechanism of Drug Action; Receptor Pharmacology. In: Essential
of Medical Pharmacology. 7th ed. India: Jaypee Brothers Medical Publishers (P) Ltd; 2014. p 40.
Receptors
Recognise
Response Drug Action
Drug Effect

15. Drug Targets- Receptors
Receptor Type Examples
G-protein coupled receptors Muscarinic receptors, adrenergic receptors
Ion channels receptors Nicotinic cholinergic, GABAA, glycine
Enzyme-linked Insulin, Epidermal Growth factor, Nerve
Growth Factor
Transmembrane JAK-STAT binding
receptors
Cytokines, growth hormone, prolactin,
interferons
Receptors regulating gene expression Steroids, Vitamin A/D

16. Drug-Receptor Interaction
• Agonist:
• Agent which activates a receptor to
produce an effect similar to that of
the physiological signal molecule
• Partial agonist:
• Agent which activates a receptor to
produce submaximal effect
• Inverse agonist:
• Agent which activates a receptor to
produce an effect in the opposite
direction to that of the agonist

17. Drug-Receptor Interaction
• Antagonist:
• Agent which prevents the
action of an agonist on a
receptor or the subsequent
response, but does not have
any effect on its own

18. Dose Response Curve

19. Dose Response Curve: Drug Potency
• Amount of drug needed
to produce a certain
response
• Position of DRC on the
dose axis
• Dictates dose of drug

20. Drug Response Curve: Drug Efficacy
•Maximal response that
can be elicited by the
drug
•Upper limit of DRC
•Dictates choice of drug

21. Therapeutic Efficacy/Clinical Effectiveness
Drug Potency Drug Efficacy
Pharmacokinetic
variables
Pathophysiological
variables
Therapeutic Efficacy / Clinical
Effectiveness

22. Therapeutic Efficacy/Clinical Effectiveness
• Expressed in terms of:
• Degree of benefit/relief afforded by the drug (in the
recommended dose range)
OR
• Success rate in achieving a defined therapeutic end point

23. Therapeutic window

24. Combined Effect of Drugs
Synergism
•Additive
• Metformin +
Glibenclamide
•Supra-additive
• Sulfamethoxazole +
trimethoprim
Antagonism
• Physical antagonism
• Charcoal + alkaloids
• Chemical antagonism
• KMnO4 + alkaloids
• Physiological antagonism
• Glucagon & insulin on blood
sugar level
• Receptor antagonism

25. Combined Effects of Drugs- Receptor
Antagonism
• Competitive equilibrium:
• Acetylcholine & Atropine
• Competitive non-equilibrium:
• Phenoxybenzamine +
adrenaline (α receptors)
• Diazepam & Bicuculline