PHARMACOEPIDEMIOLOGY

PRASHANT KOSHAL

What is Epidemiology?

Epidemiology

• Epidemiology is the study of the determinants, distribution, and frequency of disease

• 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 spared

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 medication use.

“The study of drugs as determinants of health and disease

in the general unselected population.”

Spitzer

“The application of epidemiologic knowledge, methods, and

reasoning to the study of the effects (beneficial and adverse) and

use of drugs in human populations.”

Porta and Hartzema

“The study of the use and effects of medications in

large numbers of people”

Strom

Clinical pharmacology

Pharmacoepidemiology

Epidemiology

Strom

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.

TYPEs : Epidemiology is defined as the study of the distribution and resulting determinants of diseases on populations.

Epidemiological studies can be divided into two main types:

1. Observational Study2. Intervention Study

OBSERVATIONAL VS EXPERIMENTAL STUDIES

•Observational studies , Allow nature to take its cause; the investigator measures but does not intervene.

•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 treatment)•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 EPIDEMIOLOGY

•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)

Case reports:documents unusual medical occurrence and can represent the first clues to the formulation of hypothesis, generally report a new or unique findings and previous undescribed disease. •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.

Case Series

AdvantagesUseful for hypothesis generationInformative for very rare disease with few

established risk factorsUsually of short duration.

DisadvantagesCannot study cause and effect relationshipsCannot assess disease frequency

ANALYTICAL STUDIESTwo basic designs:• Case – control or retrospective study• Cohort or prospective

NOTE• There must be a comparison group• No control No conclusion(NCNC)

CROSS-SECTIONAL STUDY• 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 NOW?”

Question: “what is happening?” no direction of inquiry

subjectsWith outcome

Without outcome

endonset time

CROSS-SECTIONAL STUDY

ADVANTAGES• Best for determining

the status quo(prevalence)

• Quick• Relatively inexpensive

DISADVANTAGES• Only a snapshot at a

time leading to a misinformation

• Response rate may be low ,with result not representative of the population

CASE CONTROL OR CASE HISTORY STUDY

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

factors.• 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

COHORT STUDY

• 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

disease• It assists in determining the temporal

relationship between the etiological factor & the disease

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

diagnostic criteria

EXPERIMENTAL STUDIES

• 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 causality

• Can be controlled or uncontrolled

CONTROLLED EXPERIMENTAL STUDIES

• In this study, a drug or procedure is compared to:1. Another drug2. Procedure3. Placebo4. Previously accepted tx• The aim is to prove the difference due to tx

CONTROLLED EXPERIMENTAL STUDIES

• Control could be:• Blind trial-single or double

A. METHODOLOGY1. Concurrent or parallel: randomized or non-

randomized(quasi)2. Sequential control: self controlled or cross over3. External control

B. STUDY POPULATION

1. Clinical trials2. Field trials3. Community trials

EXPERIMENTAL STUDIES

ADVANTAGES• Best study type• Greatest proove of causality• Gold standard for other

design• Least bias• Proves best tx or procedure

efficacy

DISADVANTAGES• Greatest expense • Long duration• Unproven facts adopted by

community can hinder study acceptance

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 or Pharmacogenetics.

• 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 interchangeably.

Drug utilization research and pharmacoepidemiology may provide insights into the following aspects of drug use and drug prescribing:

• 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 properties, affordability)

• Outcomes of use: health outcomes (benefits and adverse effects) and economic consequences.

Special applications of Pharmacoepidemiology

• Studies of Drug Utilization• Evaluating and improving physician prescribing• Drug Utilization Review • Special methodologic issues in PE studies of Vaccine

Study• PE studies of Devices• Studies of Drug induced birth defects• PE and Risk management• Use of PE to study Medication Errors• Hospital PE.

THaNK YoU ……