2. Adverse drug reaction (ADR, or adverse drug effect) is a broad term referring to unwanted,
uncomfortable, or dangerous effects that a drug may have.
An adverse drug reaction (ADR) is an unwanted or harmful reaction experienced following the
administration of a drug or combination of drugs under normal conditions of use and is suspected to
be related to the drug. An ADR will usually require the drug to be discontinued or the dose reduced.
An adverse event is harm that occurs while a patient is taking a drug, irrespective of whether the
drug is suspected to be the cause.
A side-effect is any effect caused by a drug other than the intended therapeutic effect, whether
beneficial, neutral or harmful.
The term ‘side-effect’ is often used interchangeably with ‘ADR’ although the former usually implies
an effect that is less harmful, predictable and may not even require discontinuation of therapy (e.g.
ankle oedema with vasodilators).
Drug toxicity describes adverse effects of a drug that occur because the dose or plasma concentration
has risen above the therapeutic range, either unintentionally or intentionally (drug overdose).
Drug abuse is the misuse of recreational or therapeutic drugs that may lead to addiction or
dependence, serious physiological injury (such as damage to kidneys, liver, heart), psychological
harm (abnormal behaviour patterns, hallucinations, memory loss), or death.
3.
4. Etiology
Dose-related ADRs are particularly a concern when drugs have a narrow therapeutic index
(e.g., haemorrhage with oral anticoagulants). ADRs may result from decreased drug clearance
in patients with impaired renal or hepatic function or from drug-drug interactions.
Allergic ADRs are not dose-related and require prior exposure. Allergies develop when a
drug acts as an antigen or allergen. After a patient is sensitized, subsequent exposure to the
drug produces one of several different types of allergic reaction. Clinical history and
appropriate skin tests can sometimes help predict allergic ADRs.
Idiosyncratic ADRs are unexpected ADRs that are not dose-related or allergic. They occur in
a small percentage of patients given a drug. Idiosyncrasy is an imprecise term that has been
defined as a genetically determined abnormal response to a drug, but not all idiosyncratic
reactions have a pharmacogenetic cause. The term may become obsolete as specific
mechanisms of ADRs become known.
5.
6. Symptoms
Symptoms and signs may manifest soon after the first dose or only after chronic
use.
They may obviously result from drug use or be too subtle to identify as drug-
related.
In the elderly, subtle ADRs can cause functional deterioration, changes in mental
status, failure to thrive, loss of appetite, confusion, and depression.
8. Prevention
Prevention of adverse drug reactions requires familiarity with the drug and
potential reactions to it.
Computer-based analysis should be used to check for potential drug interactions;
analysis should be repeated whenever drugs are changed or added.
Drugs and initial dosage must be carefully selected for the elderly
