• Epidemiology is the study of the
determinants, distribution, and frequency of
• Who gets disease and why
• Epidemiologists study sick and well people to
determine the crucial difference between
those who get disease and those who are
Recent data indicate that 100000
Americans die each year from Adverse
Drug Reactions, and 1.5 million US
hospitalizations each year result from
Adverse Drug Reactions; yet, 20-70% of
Adverse Drug Reactions may be
preventable. The harm that drugs can
cause has led to the development of the
field of Pharmacoepidemiology.
What Is Pharmacoepidemiology?
All drugs have adverse effects.
Pharmacoepidemilogy will never succeed
in preventing them. It can only detect
them, hopefully early, and thereby
educate health care providers and
public, which will lead to better
“The study of drugs as
determinants of health and disease
in the general unselected
“The application of epidemiologic
knowledge, methods, and
reasoning to the study of the
effects (beneficial and adverse) and
use of drugs in human
Porta and Hartzema
“The study of the use
and effects of medications in
large numbers of people”
The joining of the fields of clinical
pharmacology and epidemiology has
resulted in the development of a new
field: ‘pharmacoepidemiology’ the
study of the use of and the effects of
drugs in large numbers of people.
Epidemiology is defined as the study of the
distribution and resulting determinants of diseases on
Epidemiological studies can be divided into two main
1. Observational Study
2. Intervention Study
OBSERVATIONAL VS EXPERIMENTAL
•Observational studies , Allow nature to take its
cause; the investigator measures but does not
•Descriptive study: focuses on the description of
the occurrence of a disease in a population.
•Analytical study analyses relationships between
health status and other variables.
OBSERVATIONAL VS EXPERIMENTAL STUDIES
•Experimental or interventional studies: involve
an active attempt to change a disease
determinant(e.g an exposure or a behaviour)
or the progress of a disaese (through
•The studies are based on a group which has
had the experience compared with control
group which has not had the experience.
PURPOSE OF DESCRIPTIVE
•To generate hypothesis
•To permit evaluation of trends in health &
disease and comparisons among countries and
subgroups within countries.
•To provide a basis for planning, provision and
evaluation of health services
•To identify problems to be studied by
analytical methods and to suggest areas that
may be fruitful for investigation.
CASE STUDIES(CASE SERIES)
documents unusual medical occurrence and
can represent the first clues to the
formulation of hypothesis, generally report a
new or unique findings and previous
•Case series: collection of individual case
reports which may occur within a fairly short
time, and experience of a group of patients
with similar diagnosis.
Useful for hypothesis generation
Informative for very rare disease with few
established risk factors
Usually of short duration.
Cannot study cause and effect relationships
Cannot assess disease frequency
Two basic designs:
• Case – control or retrospective study
• Cohort or prospective
• There must be a comparison group
• No control No conclusion(NCNC)
• It is also called epidemiologic study or prevalence study.
• It analyses (describes)data collected on a group of subjects
at one point in time rather than over a period of time. i.e.
they survey exposure and disease at a single point in time.
• Both exposure and outcome variables are been evaluated at
the same point in time(without any inbuilt directionality).
• Most sophisticated descriptive study.
• It answers the question “WHAT IS HAPPENING RIGHT
Question: “what is happening?”
no direction of inquiry
• Best for determining
• Relatively inexpensive
• Only a snapshot at a
time leading to a
• Response rate may be
low ,with result not
representative of the
Advantages of case control
• It is relatively easy to carry out.
• It is also rapid and inexpensive.
• It requires comparatively few subjects.
• It can assist one in studying different etiological
• One does not need an ethical clearance.
• There is no risk to the subject .
Disadvantages of case control
• It introduces bias
• To select an appropriate control could be difficult
• It may be difficult to distinguish between the cause
of a disease and an associated factor
• A cohort is a group of people who have
something in common and remain part of a
group over an extended time
• A group of people exposed to a suspected
etiological agent are compared with a matched
control who have not been similarly exposed.
Subject selected on the basis of exposure [a
etiological factor; cigarette smoking]
• Follow-up over a period to compare the outcome
• Also a longitudinal study or prospective study
ADVANTAGES OF COHORT STUDY
• There is no bias
• The risk can be calculated bcos the incidence
can be calculated
• It is effective for studying rare exposures
• It allows the study of the natural history of the
• It assists in determining the temporal
relationship between the etiological factor &
DISADVANTAGES OF COHORT STUDY
• It takes a long time
• It is expensive
• Large no of subjects are needed
• There could be changes in the standard methods or
• Studies in which 1 group is deliberately subjected to
an experience compared with a control group with
no similar experience
• The gold standard in medicine because it proves
• Can be controlled or uncontrolled
CONTROLLED EXPERIMENTAL STUDIES
• In this study, a drug or procedure is compared to:
1. Another drug
4. Previously accepted tx
• The aim is to prove the difference due to tx
CONTROLLED EXPERIMENTAL STUDIES
• Control could be:
• Blind trial-single or double
1. Concurrent or parallel: randomized or non-
2. Sequential control: self controlled or cross over
3. External control
B. STUDY POPULATION
1. Clinical trials
2. Field trials
3. Community trials
• Best study type
• Greatest proove of causality
• Gold standard for other
• Least bias
• Proves best tx or procedure
• Greatest expense
• Long duration
• Unproven facts adopted by
community can hinder
DRUG UTILIZATION STUDY:
• Drug utilization studies aim to evaluate factors
related to the
prescribing, dispensing, administering and
taking of medication, and its associated events
(either beneficial or adverse).
• Since the early 1960’s the interest in Drug
Utilization Studies has been increasing, first with
market-only purposes, then for evaluating the
quality of medical prescription and comparing
patterns of use of specific drugs.
• The increasing importance of drug utilization
studies as a valuable investigation resource in
pharmacoepidemiology has been bridging it
with other health related areas, such as public
health, Pharmacovigilance, Pharmacoeconomics
• Drug utilization research is thus an essential part
of pharmacoepidemiology as it describes the
extent, nature and determinants of drug
exposure. In common use, the distinction
between these two terms has become less
sharp, and they are sometimes used
Drug utilization research and pharmacoepidemiology may
provide insights into the following aspects of drug use and
• Pattern of use: extent and profiles of drug use and trends in
drug use and costs over time.
• Quality of use: audits comparing actual use to national and
regional prescription guidelines or local drug formularies.
Quality indices of drug use may include the choice of drug
(compliance to recommended assortment), drug cost
(compliance to budgetary recommendations), drug dosage
(awareness of inter-individual variations in dose
requirements and age dependence), drug interaction
awareness, ADR awareness, proportion of patients being
aware of/unaware of the cost/benefit of the treatment, etc.
• Determinants of use: user characteristics (e.g.
socio-demographic parameters, attitude
towards drugs), prescriber characteristics
(e.g. specialty, education and factors
influencing therapeutic decisions), and drug
characteristics (e.g. therapeutic
• Outcomes of use: health outcomes (benefits
and adverse effects) and economic
Special applications of Pharmacoepidemiology
• Studies of Drug Utilization
• Evaluating and improving physician prescribing
• Drug Utilization Review
• Special methodologic issues in PE studies of
• PE studies of Devices
• Studies of Drug induced birth defects
• PE and Risk management
• Use of PE to study Medication Errors
• Hospital PE.