Pharmacoepidemiology is the study of the use and effects of medications in large populations. It provides estimates of drug benefits and risks in real-world populations, helping to detect adverse effects that may have been missed in pre-market clinical trials due to limited sample sizes and patient populations that do not represent those seen in practice. Pharmacoepidemiology uses epidemiological methods like cohort studies and case-control studies to understand drug effects, interactions, and outcomes in patient populations. It also includes pharmacovigilance to monitor drug safety after market approval.

1. Pharmacoepidemiology
By: Dr.Yasar Shah Page 1
PHARMACOEPIDEMIOLOGY
DEFINITIONS:
“The study of the use and effects of medications in large numbers of people”
(By: Strom)
“The application of epidemiologic knowledge, methods, and reasoning to the study of the
effects (beneficial and adverse) and use of drugs in human populations”
(By: Porta and Hartzema)
“The study of drugs as determinants of health and disease in the general unselected
population”
(By: Spitzer)
INTRODUCTION / EXPLAINATION:
Pharmacoepidemiology provides an estimate of the probability of beneficial effects of a drug
in a population and the probability of adverse effects. Although new drug products undergo the
careful scrutiny of Phase-I through Phase-III trials, some drugs are recalled soon after they are
marketed. e.g.,
 Bromfenac, recalled in 1998 due to severe hepatitis and liver failure (some requiring
transplantation).
 Cerivastatin recalled in 2001 due to Risk of rhabdomyolysis
 Propoxyphene recalled in 2010 due to increased risk of heart attacks and stroke.
 Iproniazid recalled in 1964 due to interactions with food products containing tyrosine
 Zomepirac recalled in 1983 due to Anaphylactic reactions and non-fatal allergic
reactions, renal failure
A major reason for these drug recalls is that premarketing studies treat too few patients for
uncommon effects. Therefore an adverse effect associated with drug use may go un-noticed.
Another reason that adverse events are not identified in the pre marketing drug experience is that
although subjects in pre marketing studies have the disease that the drug is targeted to treat, but
are usually devoid of other co-morbidities (such as renal failure, hepatic failure). However, in
real practice, such co-morbidities may be present. All drugs have adverse effects.
Pharmacoepidemiology 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. A lot of people die each year from Adverse Drug Reactions. The harm that drugs can cause
has led to the development of the field of Pharmacoepidemiology.
It can be called a bridge science between both clinical pharmacology and epidemiology.
Pharmacoepidemiology concentrates on clinical patient outcomes from therapeutics by using
methods of clinical epidemiology and applying them to understanding the determinants of
beneficial and adverse drug effects, effects of genetic variation on drug effect, duration-response
relationships, clinical effects of drug-drug interactions, and the effects of medication non-
adherence.

2. Pharmacoepidemiology
By: Dr.Yasar Shah Page 2
Pharmacovigilance is a part of pharmacoepidemiology that involves continual monitoring, in a
population, for unwanted effects and other safety concerns arising in drugs that are already on
the market. Pharmacoepidemiology sometimes also involves the conduct and evaluation of
programmatic efforts to improve medication use on a population basis.
Epidemiology: (see from epidemiology notes)
Definition:
Study Design:
1. Descriptive studies
2. Analytical studies
a. Observational studies
i. Case control studies
ii. Cohort studies
iii. Cross sectional studies
b. Experimental studies
i. Randomized control Trials
DRUG UTILIZATION REVIEW:
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.

3. Pharmacoepidemiology
By: Dr.Yasar Shah Page 3
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.
Methods used for conducting Drug utilization reviews:
 Using purchasing records
The simplest level of information about which medicines are being used is obtained from
purchasing records. Both hospital and community pharmacies use computerized systems for
purchase, which means these data are readily available. This gives information about
comparison between pharmacies but provides no information about medicines use.
 Using issue record
A more detailed record of use can be obtained from the medicines issued from pharmacies, to
individual patient via prescriptions or to wards in hospitals. The units used are the same as
those of purchase. Computerized systems are also used for keeping issue record. This data
may give information to the prescribers regarding their prescribing practice.
 Using prescription records
More detailed information from prescriptions, which includes the actual dose prescribed and
the concurrent medication, can be obtained in community pharmacies from patient
medication record. The extent of poly pharmacy, prescribing errors and drug interactions can
also be traced from this record.
 Using medical records and trained investigators
Examining medical record of the patients will provide information about the decisions behind the
use of particular medicines and their effectiveness. Small studies can be performed manually for
assessing the appropriate and effective use of medicines. These studies usually involve the use of
trained investigators such as Pharmacists for reviewing the medical records.
Special applications of Pharmacoepidemiology:
 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.