EFFECTS OF MEDICINES.pptx

EFFECTS OF MEDICINES
Presented to: NMT 2021
Presented by: L. Ikwanga(Bpharm)

Broad Objective
• By the end of the lesson students should acquire knowledge of basic Effects
of medications

Learning Outcomes
Learners should be able to;
1. Explain the meaning of a side effect, AE and ADRs
2. Explain basic action of the drug on receptor
3. Explain the effects of drugs which do not act on receptor

MECHANISM OF DRUG ACTION
(PHARMACODYNAMICS)
Pharmacodynamics
Pharmacodynamics is concerned with the actions, interactions and the mechanisms
(mode) of action of drugs i e what the drugs do to the body.
A drug effect is as a result of an interaction between its molecules and
some part of the tissue cells.
4

MECHANISM OF DRUGACTION
(PHARMACODYNAMICS)
• In some cases the interaction is specific and others non-specific.
• Chemical or physical properties of the drug account for the observed effects.
5

(PHARMACODYNAMICS)
Terminologies
Receptor
A macromolecule with special sites to which specific substances
bind eg drugs ( sometimes called ligands)
An Agonist
Is a drug (or hormone, neurotransmitter) which combines with its
receptor causing a conformational change in the receptor,
activates it and initiates a response.
6

(PHARMACODYNAMICS)
An Antagonist
Is a drug which binds to a receptor but does not activate it.
Also prevents the action of the agonist by making the receptor
unavailable.
A Partial Agonist
Binds to the receptor but activates it weakly and prevents the
action of a full agonist.
7

SIDE EFFECT - response to a drug which is unintended and which occurs at
doses normally used in man for prophylaxis, diagnosis or therapy of disease.
ADVERSE EVENT - any untoward medical occurrence in a patient or clinical
investigation subject administered a medicinal product and which does not
necessarily have to have a causal relationship with this treatment.
ADVERSE DRUG REACTION- response to a drug which is noxious and
unintended and which occurs at doses normally used in man for prophylaxis,
diagnosis or therapy of disease A causal relationship between the drug and the
occurrence is suspect.

(PHARMACODYNAMICS)
Naming of Receptors
Pharmacological receptors are named according to either:
(a) the principal endogenous agonist that activates them (e g
adrenoceptors, cholinoceptors, glucocorticoid receptors etc)
or:
(b) the first exogenous agonist found to activate them (e g opioid
receptors, benzodiazepine receptors etc).
9

(PHARMACODYNAMICS)
Location of drug receptors
The sites in which drug receptors are found:
1.On or within cell membranes
e g the nicotinic acetylcholine receptors, adrenoceptors
2. Inside the cells
e g cytoplasmic glucocorticoid receptors
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(PHARMACODYNAMICS)
Drugs can be divided into two categories:
(1) those acting on pharmacological receptors situated on or within the
cells.
(2) those in which the receptors are not involved.
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(PHARMACODYNAMICS)
1. Drugs which act via receptors :
(i) Act at low concentrations.
e g acetylcholine, adrenaline, noradrenaline and histamine.
(ii) React with specific receptors e g
cholinergic receptors, adrenergic receptors
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(PHARMACODYNAMICS)
(iii) They show structure-activity relationship.
(iv) Can be antagonized by specific antagonists.
13

(PHARMACODYNAMICS)
2. Drugs which do not act via receptors:
(i) Act at higher concentrations.
(ii) Do not react with specific receptors.
14

(PHARMACODYNAMICS)
(iii) Do not tend to show structure-activity relationship.
(iv) Do not have specific antagonists.
e g diethyl ether, halothane, thiazides.
15

(PHARMACODYNAMICS)
Basis of Drug Action
- Drugs do not create new functions
but
- Modify inherent functions of the tissues or cells or organs concerned.
Hence generally drugs :
- stimulate or depress cellular activity.
16

(PHARMACODYNAMICS)
- replace deficient substances.
- cause irritation.
- kill invading foreign organisms (bactericidal)
- weaken invading foreign organisms (bacteriostatic)
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(PHARMACODYNAMICS)
(1) Stimulation
Is an increase in the rate of the functional activity of a cell or tissue, e g
caffeine, amphetamine stimulate the CNS.
18

(PHARMACODYNAMICS)
(2) Depression
Denotes a reduction in such activity e g barbiturates, alcohol,
depress CNS.
(3) Replacement
When there is under production of natural substances e g Insulin
for diabetes mellitus.
19

(PHARMACODYNAMICS
(4) Irritation
Effect of drugs on nutrition, growth, morphology and functioning of
living tissues e g liniments to relieve muscle pain, and
phenolphthalein an irritant purgative.
(5) Bacteriostatic
Inhibition of bacterial growth and multiplication e g some antibiotics
20

(PHARMACODYNAMICS
(6) Bactericidal
Killing of bacteria induced by antibiotics and chemotherapeutic substances e
g. penicillins, tetracycines
21

(PHARMACODYNAMICS)
Mechanisms of action of most drugs:
1. Drug–receptor interactions (specific interactions)
(selectivity).
2. Drugs acting on an enzyme (partially specific
interactions).
22

(PHARMACODYNAMICS)
3. Non-receptor mechanisms (non- specific interactions) such as:
(i) Antimetabolites (substitution)
(ii) Chelation (e g drugs in poisoning)
(iii) Drugs affecting permeability of cell membranes
(antibiotics).
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(PHARMACODYNAMICS
(iv) Drugs acting as antiseptics (alcohol for
swabbing)
(v) Drugs acting by their physical or chemical
nature (bulking agents).
(vi) Drugs acting through antibodies (vaccines)
(vii) Placebo effects
24

(PHARMACODYNAMICS)
Potency and Efficacy
Potency
A drug is said to be potent when it posses high intrinsic activity at low unit
weight doses.
25

(PHARMACODYNAMICS)
0
20
40
60
80
100
120
1 2 3 4 5 6 7 8 9
26
Drug A Drug B
Drug A more
potent than Drug
B but have same
efficacy
Log dose
Biological
response
Drug potency

(PHARMACODYNAMICS)
• In ( fig ) Drug A is more potent than drug B, because drug A
produces same intensity as drug B at smaller doses, but both
achieve maximum response.
• Thus drug potency is useful in deciding what dose to give.
• But irrelevant in choosing which drug to use, as long as dose can be
conveniently administered e g 5mg or 500mg.
27

(PHARMACODYNAMICS)
Efficacy
• Refers to the maximum or peak response produced by a drug and is important
in drug selection process i e whether useful or not.
28

(PHARMACODYNAMICS)
0
20
40
60
80
100
120
1 2 3 4 5 6 7 8 9 10
29
Drug A
Drug B
Log dose
Biological
response
Drug efficacy
Drug A more
potent and
efficacious than
drug B

(PHARMACODYNAMICS
• (In Fig ) Drug A is not only potent, but exhibits more efficacy than drug B
because gives more maximum response.
30

(PHARMACODYNAMICS)
Drugs Acting on Enzymes
• Many drugs inhibit action of enzymes on cell membranes or inside
cells.
• Some drugs compete with the normal substrate at active site of
the enzyme, in a reversible manner.
• this is known as competitive inhibition e g allopurinol on enzyme
xanthine oxidase.
31

(PHARMACODYNAMICS)
• However some drugs combine with enzymes in irreversible manner.
• this is known as non-competitive inhibition.
32

(PHARMACODYNAMICS)
Non-receptor Mechanisms of drug action
(i) Some drugs do not act by combining with receptor sites e. g.
gastric antacids act by neutralizing Hydrochloric Acid in the
stomach.
(ii) Osmotic diuretics, like mannitol remove excess fluid from
body by increasing osmolarity of glomerular filtrate resulting in
diuresis.
33

(PHARMACODYNAMICS)
(iii) Antimetabolites:Certain antimetabolites like structural analogues of purines
and pyrimidines can be incorporated into nucleic acids disrupting their
functioning and cell division.
These antimetabolites are used in the treatment of many cancers.
34

(PHARMACODYNAMICS
(iv) Metal chelating agents like EDTA are employed in the
treatment of poisoning by heavy metals.
They stop the drug from exerting effect by forming an inactive
complex.
(v) Certain antiseptics act as protoplasmic poisons by non-
specifically acting on cells with which they come into contact.
.
35

(PHARMACODYNAMICS
(vi) Vaccines produce their effects by stimulating defence mechanisms in the
body and producing antibodies
(vii) Placebo effects of drug mechanism
• A placebo (means, I shall please) is an inactive substance given to satisfy a patient’s
demand for medicine.
36

(PHARMACODYNAMICS)
• Studies have shown that inert medicines can cure one third of all patients.
• This is termed placebo response.
37

(PHARMACODYNAMICS)
Drug concentration curve
• Time of onset - Is the time it takes for the drug to be absorbed to an extent
that the effective plasma level is reached.
• The drug should reach its site of action in sufficient quantity to produce a
response.
38

(PHARMACODYNAMICS)
As more drug is absorbed:
• the plasma level rises,
• more drug reaches site of action and
• the response increases reflecting the attainment of peak or maximum plasma level
possible for the particular dose.
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(PHARMACODYNAMICS
• As the drug is circulating in plasma elimination begins, either of the unchanged drug
molecule or its metabolites.
• The drug plasma level begins to decline and effect of drug decreases.
• Once the drug plasma level falls below the minimal level the drug action ceases although
some drug still remains in the plasma.
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(PHARMACODYNAMICS)
• Duration of Action - Corresponds to the length of time that the drug is
present in the plasma in concentrations enough to produce the desired
response.
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42
Plasma
conc.
0 1 3 4 5 6 7 8 9 10 11
Time (hrs)
Minimum effective
plasma conc.
Peak plasma conc.
T1 T2 T3 T4 T5
Drug plasma concentration curve

(PHARMACODYNAMICS)
T1 = Time of administration
T1 T2 = Time it takes to reach ‘time of onset of action’ (2
hrs)
T1 T3 = Time it takes to attain peak plasma
concentration (4hrs)
T2 T4 = Duration of effective plasma
concentration (4.6hrs)
T1 T5 = Time it takes to completely remove drug from
plasma (10hrs).
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EFFECTS OF MEDICINES.pptx

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