Download - Pharmacodynamics MBBS Class-2
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Pharmacodynamics-2Dr.U.P.Rathnakar
MD.DIH.PGDHM
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Potency & efficacy
Dose [potency]
Effect on pain [efficacy]
2mg 4mg
8mg
Mild
Moderate
Severe
15mg
25mg300mg
Drug A[Morphine]
Drug B[Pethidine]
E Max
Drug C
[Aspirin]
Potency-A>B Efficacy-A=BPotency & efficacy of C
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Drug potency & Efficacy
Potency- Amount of drug required to obtain a
particular response[More potent less dose]
Efficacy-The ability of a drug to elicit a maximal
response
Aspirin is less potent[300mg] & less efficacious than
morphine[10mg]
Pethidine is less potent[100mg] equally efficacious
as morphine[10mg]
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Dose-response curves
R
esponse
1000mg100mg10mg
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Dose-response curves determine how much of
a drug (X-axis) causes a particular effect, or a
side effect, in the body (Y-axis).
Dose-response [potency & effect]curve[DRC]
100%
50%
EC50
E max
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Graded dose response curves[Single subject- Continuous]
Advantages of Log-dose curve
Large no.of doses can be plotted on a small graph paper
Comparison of two or more drugs easier as middle portion is
straight line
Linear [Simple]dose response curve Log dose response curve
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Quantal dose response curve
Quantal or all or none: frequency with which any drug evokesa all or none response in a population
LD50 &
ED50
35% 35%
12%
3%
11%
4%
4%
15%
50%
85%
97% 100%
1
0
0
2
0
0
3
0
0
4
0
0
5
0
0
6
0
0
Cumulative DRC
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100%
50%
0
ED50 LD[TD]50
TI Narrow
TI WIDE
TI=10/5=2 TI=100/5=20
5mg
10mg
ED50
Therapeutic index
5mg 100mg
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Therapeutic range
Therapeutic range: Range between dose which
produces minimal Th.effect and Max.acceptable
adverse effect
Therapeutic range
Acceptable-ADE
Min.Th.Effect
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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
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Combined effect of drugs
Indifferent Synergism Antagonism
One facilitates the
action of other
One opposes the
action of otherAdditive
Supra-additive
[Potentiation]
Competitive
[Equilibrium &Non-equilibrium]
Non-competitive
Physical
Chemical
Physiological
Receptor
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Agonists snd antagobists
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SynergismTwo drugs One increases or facilitates the action of the other
Additive
Drug A + Drug B
= Effect of A+B [1 + 1 = 2]
Advantage:
Side effect may not add up
Dose of both can be reduced
Eg.
Aspirin + Paracetamol
Nitrous oxide +Halothane
Amlodipine+Atenolol
Supra-additive (Potentiation)
Effect of combination is
more than individual effect
of 2 drugs 1 + 1 = 3 OR 1 + 0 = 2
One drug may be inactive
Levodopa+Carbidopa[Inacti
ve alone][1 + 0 = 2] Sulfamethaoxazole+Trimeth
oprim[Both active] [1+1= 3]
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Antagonism
[Effect of one drug is decreased]
1. Physical Charcoal adsorbs alkaloids
2. Chemical KMno4 oxidizes Alkaloids
BAL chelates arsenic
Protamine neutralizes heparin
Na.Thiopentone+ Succinylcholine
3. Physiological Histamine and Adrenaline
[Functional] Glucagon and Insulin
Hydrochlorothiazide and triamterene
4. Receptor:
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Antagonism [Receptor]
One[Antagonist] blocks the receptor action of the other[Agonist]
Competitive[surmountable]
Binds with the same site on
the receptor
Resembles the agonist Surmountable by increasing
the concn. Of agonist
Rightward shift of DRC
5. Eg.
Ach atropine
Morphine - Naloxone
Non-competitive[unsurmountable]
Binds to another site or
same site covalently
No resemblance Not surmountable
Flattening of DRC
Eg.
Diazepam Bicuculline
Phenoxybenzamine-
Noradrenaline
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Competitive and non-competitive antagonism
Rightward shift
of DRC
Flattening of DRC
Competitive Non competitive
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Competitive Non-competitive
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Factors modifying fuel efficiency???
Factors modifying drug action
New
DriverMfr.defect
Bad road
Over loaded
Engine problem
Tarffic congestion
[Age?]
[M or F][Genetic?]
[Envn.]
[Obesity?]
[Patho.states]
[DI, polypharmacy]