pharmacodynamics

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