Pharmacoepidemiology lectures
Introduction to Pharmacoepidemiology
Epidemiology is the science that studies the occurrence of diseases in large populations of people as
a function of determinants. Epidemiology is an essential science for the conduct of evidence based
medicine. There are two sides of the coin, etiology and diagnosis. Ethological and intervention are
causal associations, smoking causes lung cancer, these are analytical studies, case-control, it focusses
on mostly 1 determinant, confounding bias and explanatory statistical models are used. Diagnostic
and prognostic are predictive associations, descriptive studies, cohort design, there are more
determinants, there is no confounding bias and predictive statistical models are used.
The objects of research are ethological research, diagnostic research, prognostic research and
intervention research.
For drug development there is a circular model,
starting with a mechanism of disease for which a
drug must be discovered, this drug is than
characterized and formulated to bring it onto
the market. Post-marketing
pharmacoepidemiology is then done to analyse
all deaths and injuries which is a mechanism of
disease again.
Pharmaco-epidemiology is the scientific field
that studies the contribution of drugs in disease
prevention and therapy in large population.
The reasons that drugs have dangerous side effects and are withdrawn are the clinical trials are not
large enough, the drug use differs from the trials, time plays a role and off-label prescribing may
bring up unexpected issues.
There are different phases of drug development, there are pre-clinical phases, clinical phases 1, 2 and
3 and post-marketing phase 4. A type 1 question contains the drug, patient and age and sex. A type 2
question contains the drug, disease and outcome. For epidemiological studies there are experimental
studies and observational studies. Experimental studies are clinical trials (RCT), community
intervention trials and field trials. Observational studies are descriptive studies and case-control
studies. In clinical trials there is limited number of patients, limited time, homogenous population
and other variables are excluded or controlled. Observational studies have large number of patients,
unlimited time, contains drug-users in practice and does have other influences like smoking, drugs
and nutrition.
To talk about the effects the following terms are used. Efficacy is the effect in clinical trials or
laboratory studies. Effectiveness is the effect in daily practice and efficiency the costs in relation to
effects.
Post-marketing surveillance is the monitoring off all desirable and undesirable effects of drugs to
health after the drug has been released on the market. The goal of this study is to obtain scientifically
based data on rational and safe use of drugs. This makes the drugs more transparent on the adverse
effects. The patient, pharmacist, insurance company, government and industry are interested in the
post-marketing surveillance in order to asses the quality of the product. Post-marketing surveillance
are made via spontaneous reporting systems, routine databases, questionnaires and cohorts.
, ATC coding is the anatomical therapeutic chemical
classification system. It has 7 positions, as can be
seen in the scheme.
The defined daily dose (DDD) is given as a dose that
is standard and derived from phase III in clinical
trials. It is the average daily maintenance dose for a drug used for its main indication in adults. It does
not consist of any patient information but it is a rough estimate. The DDD is revised after three years.
It is mainly used to compare volumes of drug use at population level. If the prescribed DDD is much
lower than 1 there will be little to no therapeutic effect. If the prescribed DDD is much higher than 1
there will be too much drug in the system leading to adverse effects.
Adverse effects will be reported following the yellow card system, this will be done by several
members however the general partitioner and the pharmacists will mostly report these. The
problems in spontaneous reporting systems can be weber effect, there are more reports on new
drugs. Channelling phenomenon happens because a drugs ‘seems’ better but when put to the test
this will not show a difference in side effects. Media attention can also influence the amount of
spontaneous reporting by giving the attention to the drug. Encepp has excess to large patient
databases across various European countries. In the encepp there is a lot of protocolled research.
Cohort studies are set up with a goal. The advantages of these studies is that the data is there
already in large numbers, validation data, prevents recall bias, information about reference groups,
low costs and minimal effort for researcher. The disadvantage is indication bias, insufficient number
of patients, new drug (channelling), no information about confounding variables and validity and
completeness data depended on data source.
From a pharmaco-economical perspective, drugs are expensive so a decision model needs to be
designed, this will assess the efficiency and perspective and determine the cost-effectiveness.
Pharmacoeconomics and evaluation
Health economics is the application of economic science to a topic in healthcare.
Pharmacoeconomics is meant to be economic evaluation of medication with medication. Health
technology assessment roots in different disciplines and aims to perform a complete assessment of a
health intervention, including cost-effectiveness.
In European countries the role of the HTA varies. When present in decision making its role is for
medicines, vaccines and population screening programs. They are less involved for devices, medical
procedures. There are however large differences among countries. For low middle income countries
a large part of health care spending is out of their own income this can bankrupt families. WHO
therefore proposes universal health coverage. Pharmaceutical care and specialist care is one of the
largest spending of the health care in general. Because some medicine are so expensive this puts the
patients and health carers for hard choices. Some drugs can be reimbursed but then from whom and
to what degree should be reimbursed. Different countries can have different approaches to this.
Cost-effectiveness is the degree to which something is effective or productive in
relation to its cost. The cost-effectiveness is always compared to an alternative. It is
the ‘value for the money’, for example the € per life year gained for new cancer
treatment. Funding a new treatment requires money, this money can be raised by
increasing taxes, increasing insurance premium or reducing costs for other treatments (opportunity
costs), this is trading health for health. In the Dutch healthcare system there are different thresholds
depending on the disease treated, these are 20.000/50.000/80.000 per QALY. In hospital care this is