Pharmacodynamics is the study of how drugs act on the body and their mechanisms of action. Drugs can act through receptors, enzymes, ion channels, or physical properties. Receptors are molecules that drugs bind to, like G-protein coupled receptors, inducing cellular changes. Affinity is a drug's ability to bind receptors, while intrinsic activity is its ability to produce an effect after binding. Agonists fully activate receptors, antagonists block receptors' effects. Drug efficacy is the maximum effect, while potency is the amount needed to produce an effect. Drug actions can be modified by factors like age, genetics, psychological state, diseases, other drugs, and tolerance from repeated use.

1. *

2. *Pharmacodynamics
* What drug does to the body?
* The study of physiological and
biochemical effects of drugs and their
mechanism of action at organ
system/subcellular/ macromolecular
levels

3. -It includes
* Mechanism of drug action
* Other pharmacological actions
* Dose-effect relationship
* Combined effect of drugs

4. Targets of drug
action
Receptors
Physical/chemical
property
Transporters
Ion
channels
Enzymes
Non receptor

5. *Enzymes
Drug
Enzyme
Stimulation
Enzyme
Inhibition
Stimulation - Pyridoxine stimulates
decarboxylase
Inhibition - Allopurinol inhibits xanthine
oxidase

6. *Ion channels
* Drugs can directly bind to ion
channels
* Can affect ion movement through it
* E.g. – Local anesthetic obstruct
voltage sensitive Na + channels
- Nifedipine blocks L-type Ca2+
channels

7. * Act by virtue of their physical/chemical
property
* e.g. 1. Activated charcoal – adsorptive
2. Dimercaprol – chelating
*Physical/chemical property

8. *Receptors
Macrolecules present either on the cell
surface, cytoplasm, or in the nucleus
where the drug binds and interact to
produce cellular changes.

9. Receptors
G-protein
coupled
Enzyme-linked receptors
Receptors with intrinsic
ion channels
Nuclear receptors

10. * Affinity – The ability of the drug to
bind with the receptor
* Intrinsic activity – the
ability of the drug to produce
pharmacological action after binding to
the receptor

11. * Agonist – A drug capable of producing
pharmacological action after binding to the
receptor.
Has both affinity & maximal intrinsic activity
E.g. adrenaline, histamine
* Competitive antagonist – Drug that binds
to the receptor but cannot produce any
action.
Has affinity and no intrinsic activity
E.g. Propranolol, atropine

12. * Non-competitive antagonist – Drug binds to
the different site on same receptor and alters
receptor in such a way that agonist can no
longer bind to it.
e.g. bicuculline
* Drug efficacy – It is maximum effect of the
drug.
* Drug potency – the quantity of a drug
required to produce a desired response is
potency.

13. *Synergism
* When the action of one drug is
facilitated or increased by the other
they are said to be synergistic
1. Acetylcholine + physostigmine
2. Levodopa + carbidopa

14. * Factors modifying drug action
1. Age :
 Neonates
* Hepatic and renal functions are not fully developed-
less metabolism & less excretion of drug - toxicity
e.g. Chloramphenicol – gray baby syndrome in infants

15.  Elderly –
* Hepatic and renal functions decline -
less metabolism & less excretion of drug - toxicity
e.g Aminoglycoside can cause more nephrotoxicity &
ototoxicity hence dose is reduced

16. 2. Genetics : These factors influence drug
metaboism, action
Succinylcholine causes - succinylcholine apnoea in
patients with atypical pseudocholinesterase
Sulfonamides causes – hemolysis in G6PD
deficiency

17. 3. Psychological states :
Belief, expectation, personality of patient and
attitude, personality of the doctor – influence drug
effect
Anxious cases – requires more anesthetic dose
 Neurotics require larger dose of diazepam

18.  Some patients respond to placebo
- Placebo is a inert substance or dummy medicine
having no pharmacological action
Effect of placebo depends on
- Patient
- Drug
- Physician

19. 4. Pathological states :
GI disorders
* Malabsorption syndrome – absorption of some drugs
reduced
Liver disease –
* Chronic liver disease - decreased metabolism
e.g propranolol

20.  Renal failure –
* Decreased excretion – toxicity
e.g Aminoglycosides

21. 5. Presence of other drugs :Modification of one
drug response by another, when administered
together or in quick succession
 Drug interactions
 Antacids + iron – forms complex, unabsorbed
 Penicillin + probenecid – Probenecid inhibits
excretion of penicillin

22. 6.Tolerance
Repeated administration of certain drugs can
results in decrease in their pharmacological
effect. Higher doses of such drugs are
required to produce a given response.
e.g. Ephedrine – bronchial asthma
Nitrates – angina pectoris