Adverse effects of drugs

1. 1.3.5 UNDESIRABLE DRUG
EFFECTS

2. UNDESIRABLE DRUG EFFECTS
LEARNING OBJECTIVES:
1. Definition of undesirable drug effects
2. To describe the different types of undesirable
drug effects
3. What should a practitioner do in case of
undesirable drug effects

3. INTRODUCTION:
All drugs can produce unwanted effects
Undesirable effects can be classified into several groups
depending on their nature and mechanisms underlying
them
The undesirable effects are referred to as adverse effects
if they are harmful
UNDESIRABLE DRUG EFFECTS

4. INTRODUCTION …. CONT’D:
Broadly, adverse drug effects can be classified into two
categories
1. Adverse effects related to the main pharmacological
action of the drug e.g. side effects
2. Adverse effects unrelated to the main
pharmacological action of the drug e.g. allergic
reactions
UNDESIRABLE DRUG EFFECTS

5. ADVERSE DRUG EVENT
• This is a general broad term that describes any adverse
outcome to medication administration
• An Adverse Drug Event is defined as ‘any noxious or
undesirable (unintended) medical occurrence associated
with the use of a drug in humans for prophylaxis, diagnosis
and therapy’.
• Serious Adverse Event: - Any event that results in any of
the following: death, life-threatening event/reaction,
requires/prolongs hospitalization, permanent or significant
disability/incapacity, congenital anomaly/birth defect, or
requires intervention to prevent permanent
impairment/damage
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6. ADVERSE EFFECT
• An Adverse Effect is an undesired harmful effect
resulting from use of medication needed for
prophylaxis, diagnosis and therapy
• Includes allergic reactions, adverse drug reactions,
harmful effects resulting from overdose and lack of
efficacy
• Types can be classified with the acronym - ABCDEF
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7. ADVERSE DRUG REACTION
An Adverse Drug Reaction is a response to a drug
which is harmful and unintended, and which occurs at
doses normally used in man (definition according to
WHO).
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8. SIDE EFFECT
• A Side Effect is any unintended effect of a drug
occurring at doses normally used in man, which is
related to the pharmacological properties of the drug
• Side effects are secondary unwanted effects that
occur due to drug therapy
• Side effects are an extension of the pharmacological
drug effects and are seen with therapeutic doses
• Side effects are dose-related, predictable and can
occur in all people
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9. TOXIC EFFECT
• A Toxic Effect is an intense pharmacological effect
that occurs at high dose or after prolonged drug
administration and is harmful
• Toxic drug effects are predictable and dose-
dependent
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10. Types of ADRs
Type A- Augmented
• Dose dependent
• Pharmacological dependent
• E.g. Hypoglycemia due to insulin, Bleeding due to
anticoagulants
• What to do- reduce the dose, avoid concomitant
use of drugs with similar actions

11. Type B- Bizzare
• This type is unpredictable ADRs
• Not dose related
• E.g. Hypersensitivity reactions to penicillin,
Stephen Johnson Syndrome
• What to do- stop therapy, avoid use in future and
advise patient to report

12. Type C ADRs
• ADRs due to chronic use of the drug
• E.g. use of steroids may lead to adrenal
suppression
• Use of analgesics may also lead to analgesic
nephropathy

13. Type D- e.g. TERATOGENIC EFFECT
• A Teratogenic Effect is a drug induced birth
defect as a result of drug therapy during pregnancy
e.g. Adenocarcinoma of vaginal which may appear at
puberty after taking Diethylstilbestrol during
pregnancy
• The most vulnerable period for teratogenesis is the
period of organogenesis (day 17 to 60 of gestation)
• During the first two weeks of gestation, teratogenic
agents usually kill the embryo rather than cause
congenital malformations
• The degree and type of teratogenicity is determined
by the drug dose, duration of exposure and timing of
exposure
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14. Type E- End of Dose (Withdraw Reactions)
• ADRs when the drug is withdrawn abruptly or stopped e.g.
Opioids
• Abrupt discontinuation or decrease in the dosage of some
drugs results in development of undesirable effects known
as withdrawal reactions
• Withdrawal reactions occur due to the physiological
adaptation that occurs with prolonged exposure to the
drug.
• Withdrawal reactions usually occur following prolonged
usage of a drug and include withdrawal syndromes and
rebound effects
• What to do- tapper the drug

15. Type F- Failure of the Drug
E.g. Oral contraceptive- they may be come ineffective
if given with drugs that affect their metabolism

16. IDIOSYNCRATIC REACTION
• An Idiosyncratic Reaction is a genetically
determined abnormal reaction to a drug
• The reaction is unusual, unexpected and is not dose-
related
• In some cases, the individual may be highly sensitive
even to low doses of the drug or highly insensitive
even to high doses of the drug
• Sometimes the person will react with the opposite
effect to the desired one (also called paradoxical
reaction)
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17. ALLERGIC DRUG REACTION (HYPERSENSITIVITY
REACTION)
• An Allergic Drug Reaction is an immunologically
mediated reaction to a drug
• Drugs can cause allergic reactions via both humoral
and cell-mediated immunity
• Drugs can cause all the four types of allergic reactions
(Types I, II, III and IV)
• Allergic drug reactions are not pharmacologically
predictable and are not dose dependent
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18. DRUG INTOLERANCE
• Drug Intolerance is the inability of a person to
tolerate a drug
• The individual shows an exaggerated response to
even small doses of the drug
• Drug intolerance is unpredictable
• Drug intolerance could also be qualitative (e.g.
idiosyncrasy and allergic reactions)
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19. GENOTOXICITY: MUTAGENICITY AND
CARCINOGENICITY
• Some drugs are genotoxic i.e. they alter DNA
• Such drugs are mutagenic i.e. they can cause
mutations (a mutation is a change in the genotype of a
cell that is passed on when the cell divides)
• Some mutagenic drugs are carcinogenic (mutagenesis
is the first step in the process of carcionogenesis)
• Drugs produce mutations by forming covalent bonds
with DNA
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20. UNEXPECTED FAILURE OF EFFICACY
These reactions occur when there is a failure of efficacy of a
drug
Such reactions are common, and are caused by a number of
factors including:
• Pharmacokinetic factors e.g. poor absorption
• Pharmacodynamic factors e.g. abnormalities in drug
molecular targets
• Inadequate dosing
• Drug resistance
• Drug tolerance
• Drug interactions
• Substandard drugs
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21. END OF TREATMENT REACTIONS: WITHDRAWAL
REACTIONS
• Withdrawal syndrome refers to the characteristic
clinical features that occur upon abrupt drug cessation,
and are often opposite to the effects of the drug that was
being taken
• Rebound effect is a type of withdrawal during which
symptoms that were suppressed or treated by the drug
re-emerge when the drug is discontinued or reduced in
dosage
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22. DRUG DEPENDENCE
• Drugs that influence the behaviour and mood are
often misused to obtain pleasurable effects
• Repeated use of such drugs results in dependence
• Drug dependence is a state of compulsive use of drugs
and is also referred to as drug addiction
• Dependence could be “psychological” or “physical
(physiological)”
• Psychological dependence is compulsive drug-seeking
behaviour to obtain its pleasurable effects
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23. DRUG DEPENDENCE …. CONT’D
Physical dependence
• Physical dependence is said to be present when
withdrawal of the drug produces adverse symptoms
• The body undergoes physiological changes to adapt
itself to the continued presence of the drug in the body
• Stopping the drug results in “withdrawal syndrome”.
The symptoms of withdrawal syndrome are distressing
and the person then craves for the drug
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