2. Adverse Drug Reactions
(ADR)
Harm associated with the use of a given
medications
OR
Unwanted or harmful reaction
experienced after the administration of a
drug or combination of drugs under normal
conditions of use
www.mcqsinpharmacology.com
3. ADR= significant morbidity & mortality
Range from mild reactions
(drowsiness, nausea, itching& rash);
disappear after discontinuation of drug
OR
Severe reactions (respiratory
depression, neutorpenia, hepatocellualr
injury, hemorrhage, anaphylaxis
www.mcqsinpharmacology.com
4. ADR most common in
Women
Elderly (>60 y old)
Very young (1-4 y)
Patients taking more than one drug
www.mcqsinpharmacology.com
5. Classification of ADR
Rawlin & Thompson classification ABCD
Traditional classification A & B
About 80% of ADR----Type A reactions
1) Type A Reactions
a) Related to pharmacological action of drug
Extensions of the principal pharmacological action
of the drug
Cont.
www.mcqsinpharmacology.com
6. b) Predictable
Relatively easily predicted by preclinical and clinical
pharmacological studies
c) Common
Type A reactions not serious---common
d) Dose-dependent
Usually dose dependent
www.mcqsinpharmacology.com
7. Type A reactions
(classes)
i) Toxicity of overdose (Drug overdose)
An adverse drug reaction caused by excessive
dosing
e.g., hepatic failure with dose of paracetamol
Headache with antihypertensives
hypoglycemia with sulfonylurea;
www.mcqsinpharmacology.com
8. ii) Side Effects
Nearly unavoidable secondary drug effect
produced by therapeutic doses
intensity is dose dependent
Occur immediately after initially taking drug or may
not appear until weeks after initiation of drug use
E.g., sedation with antihistamines
www.mcqsinpharmacology.com
9. iii) Secondary Effects
Secondary pharmacological effect
E.g., development of diarrhea with antibiotic therapy
due to altered GIT bacterial flora
Orthostatic hypotension with a phenothiazine
www.mcqsinpharmacology.com
10. iv) Drug Interactions
When two drugs taken together & they effect each
other’s response pharmacologically or kinetically
E.g., one drug slow metabolism of 2nd
drug blood
conc.= toxicity
Theophylline toxicity in presence of erythromycin
www.mcqsinpharmacology.com
11. 2) Type B Reactions
Unrelated to known pharmacological
actions of drug
Unpredictable
Often caused by immunological &
pharmacogenetic mechanisms
Unrelated to dosage
Comparatively rare & cause serious illness
or death cont.
www.mcqsinpharmacology.com
12. Results (more likely) in withdrawal of
marketing authorization
Often not discovered until after drug is
marketed
Both environmental & genetic factors =
important in this reaction
www.mcqsinpharmacology.com
13. Type B Reactions (classes)
i) Drug Intolerance
Lower threshold to normal pharmacological action of a
drug
e.g., tinnitus (single average dose of aspirin)
ii) Hypersensitivity (immunological reaction)
Immune mediated response to a drug agent in
sensitized patient
e.g., anaphylaxis with penicillin
www.mcqsinpharmacology.com
14. iii) Pseudoallergic Reaction
Direct mast cell activation & degranulation by
drugs (opiates, vancomycin & radiocontrast media)
Clinically indistinguishable form Type I
hypersensitivity but not involve IgE (non
immunologic reactions)
www.mcqsinpharmacology.com
15. iv) Idiosyncratic Reactions
An uncommon & abnormal response to drug
Usually due to genetic abnormality
Affect drug metabolism & receptor sensitivity
Harmful even fatal, appear in low doses
E.g., Anemia (hemolysis) by antioxidant drugs
(G6PD deficiency)
Paralysis due to succinylcholine (enzyme
deficiency)
www.mcqsinpharmacology.com
16. 3) Type C (chronic) Reactions
Associated with long-term drug therapy
Well known and can be anticipated
Adaptation occurs = discontinuation of
drug=abstinence syndrome
E.g. opoids, alcohol, barbiturates
www.mcqsinpharmacology.com
17. 4) Type D (delayed) Reactions
Carcinogenic & teratogenic effects
Delayed in onset
Very rare
Carcinogenic Effect
Medication lead to cancer; take >20 y to develop
Teratogenic Effect
Drug- induced birth defects
www.mcqsinpharmacology.com
18. Sign & Symptoms of ADR
Mild, moderate, severe or lethal
Sign & symptoms manifest soon after 1st
dose or
only after chronic use
e.g., Allergic reactions occur soon after drug is taken
usually 2nd
time ( itching, rash, eruption, upper or lower
airway edema with dyspnea & hypotension)
Idiosyncratic reactions=any unpredicted symptom
www.mcqsinpharmacology.com
19. Mechanisms of ADR
Type A =non immunological, reversible with
reduction of dose, non serious, extension of
pharmacological effects
Type B
Biochemical mechanism unrelated to
pharmacological
Immunologic = Hypersensitivity (Type I, II, III, IV)
OR
Non immunologic (direct)= Pseudoallergic,
idiosyncratic, intolerance www.mcqsinpharmacology.com
20. Mechanism of Type B
Reactions
i) Often mediated by a chemically
reactive metabolite
Non detoxification of metabolite
Direct cytotoxicity
Direct tissue damage + necrosis
www.mcqsinpharmacology.com
21. Drug Hypersensitivity
(allergic) Reaction
Common form of adverse response to drugs
Classification (Gell & Coombs)
Type I reactions (IgE-mediated)
Type II reactions (cytotoxic)
Type III reactions (immune complex)
Type IV (delayed, cell mediated)
www.mcqsinpharmacology.com