Adverse Drug Reactions (ADRs)

Adverse Drug Reactions (ADRs) are harmful or unintended effects of medicines occurring at normal therapeutic doses.

Definition of Adverse Drug Reactions (ADRs):

• An adverse drug reaction is an unintended and harmful response to a drug that occurs at normal therapeutic doses used in humans for prophylaxis, diagnosis, or treatment.

Classification of ADRs:

1. Type A (Augmented)

   • Dose-dependent and predictable
   • Related to the known pharmacological action of the drug
   • Usually mild and preventable
   • Examples:
   • Hypoglycemia from insulin
   • Bleeding from warfarin

2. Type B (Bizarre)

   • Unpredictable, not dose-related
   • Often immune-mediated or idiosyncratic
   • More severe and sometimes life-threatening
   • Examples:
   • Anaphylaxis to penicillin
   • Stevens–Johnson syndrome from sulfonamides

3. Type C (Chronic)

   • Occurs during long-term therapy
   • Related to cumulative dose
   • Examples:
   • Adrenal suppression from long-term corticosteroid use

4. Type D (Delayed)

   • Appears after a prolonged period following drug use
   • Examples:
   • Carcinogenesis after chemotherapy
   • Teratogenic effects from thalidomide

5. Type E (End of use)

   • Related to withdrawal effects after discontinuation of a drug
   • Examples:
   • Rebound hypertension after stopping clonidine

6. Type F (Failure of therapy)

   • Unexpected lack of effectiveness of a drug
   • Often due to resistance, poor compliance, or wrong dosage

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