Adverse Drug Reactions (ADR) and Types of ADRs

An Adverse Drug Reaction (ADR) is a harmful, unintended, and unwanted response to a medicine occurring at doses normally used for the prevention, diagnosis, or treatment of a disease. ADRs are an important concern in healthcare because they may reduce treatment effectiveness, increase healthcare costs, prolong hospitalisation, and, in severe cases, may be life-threatening. Pharmacists play an important role in identifying, preventing, documenting, and reporting ADRs through pharmacovigilance.

Types of Adverse Drug Reactions

ADRs are commonly classified into the following types:

1. Type A – Augmented Reactions:
These are dose-dependent and predictable reactions related to the known pharmacological action of a drug. They are usually common and can often be prevented by dose adjustment. Examples include hypoglycaemia caused by insulin and bleeding caused by anticoagulants.

2. Type B – Bizarre Reactions:
These reactions are unpredictable and generally not dose-dependent. They are often associated with allergic or idiosyncratic responses. Examples include anaphylaxis caused by penicillin and severe skin reactions due to certain medicines.

3. Type C – Chronic Reactions:
These occur due to long-term or prolonged drug therapy and are generally related to the duration of treatment. Examples include adrenal suppression following prolonged corticosteroid therapy and dependence caused by some drugs.

4. Type D – Delayed Reactions:
These reactions become apparent after some time, even after the drug has been used or discontinued. Examples include certain drug-induced cancers and teratogenic effects.

5. Type E – End-of-Use Reactions:
These occur mainly due to withdrawal of a medicine, particularly after prolonged use. Examples include withdrawal symptoms after stopping corticosteroids or certain CNS-active medicines abruptly.

6. Type F – Failure of Therapy:
These occur when a drug fails to produce the intended therapeutic effect, sometimes because of drug interactions, resistance, or inappropriate dosing.

Understanding the different types of ADRs helps healthcare professionals recognise adverse effects promptly and improve the safety and effectiveness of medication therapy.

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