UNIT 3- Adverse Drug Reaction
ADR:
Adverse drug reactions (ADRs) are considered as one among the leading causes of morbidity and mortality
• The epidemiological importance of ADR is justified by its high prevalence rate since
➢they cause from 3% to 6% of hospital admissions at any age, and up to 24% in the elderly population ➢they rank fifth among all causes of death
➢they represent from 5 to 10% of hospital costs 21/09/2025 2
• Every occasion when a patient is exposed to a medical product, is a unique situation and we can never be certain about what might happen.
• A good example for this is thalidomide tragedy in late 1950s and 1960s.
• Thalidomide prescribed as a safe hypnotic to many thousands of pregnant women caused severe form of limb abnormality known as phocomelia in many of the babies born to those women.
• WHO defines ADR as ‘Any response to a drug which is noxious and unintended, and which occurs at doses normally used in man for prophylaxis, diagnosis, or therapy of disease, or for the modification of physiological function’.
• serious adverse event (events relating to drugs or devices) as one in which “the patient outcome is death, life-threatening (real risk of dying), hospitalization (initial or prolonged), disability (significant, persistent, or permanent), congenital anomaly, or required intervention to prevent permanent impairment or damage.
Classification of ADRs
Rawlins-Thompson classification
DoTS system
• DoTS system is based on Dose
relatedness, Timing and patient
Susceptibility
• In contrast to Rawlins–Thompson
classification, which is defined only by the
properties of the drug and the reaction, the
DoTS classification provides a useful template
to examine the various factors that both
describe a reaction and influence an
individual patient's susceptibility.
1. Dose Related
• DoTS first considers the dose of the
drug, as many adverse effects are
clearly related to the dose of the drug
used.
• For example, increasing the dose of a
cardiac glycoside will increase the risk of
digitalis toxicity.
In DoTS, reactions are divided into
➢Toxic effects (effects related to the use
of drugs outside of their usual therapeutic
dosage),
➢Collateral effects (effects occurring
within the normal therapeutic use of the
drug) and
➢Hyper-susceptibility reactions
(reactions occurring in sub-therapeutic
doses in susceptible patients).
• Collateral effects include reactions not
related to the expected pharmacological
effect of the drug or off-target reactions of
the expected therapeutic effect in other
body systems.
• It is worth noting that approximately 20%
of newly marketed drugs have their
dosage recommendations reduced after
marketing, often due to drug toxicity.
• The time course of a drug's presence at
the site of action can influence the
likelihood of an ADR occurring.
• For example, rapid infusion of furosemide
is associated with transient hearing loss
and tinnitus, and a constant low dose of
methotrexate is more toxic than
equivalent intermittent bolus doses
