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ADVERSE DRUG REACTIONS. DR. SHABANA ALI. 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.

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adverse drug reactions



adverse drug reactions adr
Adverse Drug Reactions (ADR)

Harm associated with the use of a given medications


  • Unwanted or harmful reaction experienced after the administration of a drug or combination of drugs under normal conditions of use

ADR= significant morbidity & mortality

  • Range from mild reactions (drowsiness, nausea, itching& rash); disappear after discontinuation of drug


  • Severe reactions(respiratory depression, neutorpenia, hepatocellualr injury, hemorrhage, anaphylaxis

ADR most common in

  • Women
  • Elderly (>60 y old)
  • Very young (1-4 y)
  • Patients taking more than one drug
classification of adr
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.

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

type a reactions classes
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;

ii side effects
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
iii secondary effects
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
iv drug interactions
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
2 type b reactions
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.

Results (more likely) in withdrawal of marketing authorization

  • Often not discovered until after drug is marketed
  • Both environmental & genetic factors = important in this reaction
type b reactions classes
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

iii pseudoallergic reaction
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)
iv idiosyncratic reactions
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)

3 type c chronic reactions
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

4 type d delayed reactions
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

sign symptoms of adr
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

mechanisms of adr
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)


Non immunologic (direct)= Pseudoallergic, idiosyncratic, intolerance

mechanism of type b reactions
Mechanism of Type B Reactions

i) Often mediated by a chemically reactive metabolite

Non detoxification of metabolite

Direct cytotoxicity

Direct tissue damage + necrosis


ii) Bind to NA altered gene product

  • Bind to a larger macromolecule inducing immune response (produce Ab & bind to Ab)
drug hypersensitivity allergic reaction
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)