Clinical studies are scientific investigations to examine and evaluate
the efficacy and safety of therapeutic procedures or
drugs using human subjects. According to their designs, they are
classified into several types.
Treatment studies
Randomized controlled trial
Double-blind randomized trial
Single-blind randomized trial
Non-blind trial
Nonrandomized
trial
Observational studies
Cohort study
Prospective cohort
Retrospective cohort
Time series study
Case-control study
: A case-control study is designed to help determine
if an exposure is associated with an outcome. These studies compare
patients who have a disease or outcome of interest (cases) with
patients who do not have the disease or outcome (controls), and looks
back retrospectively to compare how frequently the exposure to a risk
factor is present in each group to determine the relationship between
the risk factor and the disease.
Nested case-control study
Case
report
Phases of Trial
Drug trials can be
classified into four phases, a classification which is widely used by
the pharmaceutical industry.
Phase
I usually tests the effects of a new drug in healthy
volunteers or patients unresponsive to usual therapies. They look at
how the drug is handled in the human body
(pharmacokinetics/pharmacodynamics), particularly with respect to the
immediate short-term safety of higher doses.
Phase
II examines dose-response curves in patients and what
benefits might be seen in a small group of patients with a particular
disease.
Phase
III examines a new drug is tested in a controlled fashion
in a large patient population against a placebo or standard therapy.
This is a key phase, where a drug will either make or break its
reputation with respect to safety and efficacy before marketing begins.
A positive study in Phase III is often known as a landmark study for a
drug, through which it might gain a license to be prescribed for n
specific disease.
Phase
IV is often called a postmarketing study as the drug has
already been granted regulatory approval license. These studies are
crucial for gathering additional safety information from a larger group
of patients in order to understand the long-term safety of the drug and
appreciate drug interactions.
Classification of Trials
by Design
Patients may be
assigned to the new treatment or to the standard treatment by
several methods.
Parallel-group
trial is the most commonly used study
design. When using "parallel groups", each patient receives
one treatment.
Crossover
trial: All the patients change their initial group during
study, and eventually get all treatments in varying order. Thus, each
patients beconme his/her own control.
Factorial
trials assign patients to more than one
treatment-comparison
group. These are randomized in one trial at the same time, ie, while
treatment A is being tested against placebo, patients are re-randomized
to tretment B or placebo, making four possible treatment combinations
in total.
Cluster
randomized trials are performed when larger groups (e.g.,
patients of a single practitioner or hospital) are randomized instead
of individual patients.
Classification of Trials
by the Number of Centers
Single-center studies are mainly used tor Phase I and II
studies.
Multicenter studies can be carried out at any stage of
clinical development. Muhicenter studies are necessary for evaluating a
new medication or procedure more efficiently in terms of accruing
sufficient subjects over a shorter period of time, and to
provide a better basis for the subsequent generalization of the trial's
findings.
Classification of Trials
by the Expected Result
Trials can also be
described as superiority studies, equivalence studies, or
noninferiority studies in terms of what the study was designed to prove.
Superiority
studies are designed to demonstrate that one treatment
(generally the new one) is more effective than another (generally
placebo or current best treatment). Most clinical trials
belong to this category.
Equivalence
study are designed to prove that one treatment is as
effective as another. Hence, the trial should demonstrate that
the effect of the new drug
differs from the effect of the current treatment by a margin that is
clinically unimportant
Non-inferiority
studies are designed to demonstrate that the effect of a new
treatment cannot be said to be significantly weaker than that of the
current treatment. In the latter twostudy types the new
treatment might still turn out to be more effective than the
comparative treatment, but this is not the prior assumption or
hypothesis of the trials.
Classification of Trials
by the Originality of the Result
Exploratory study: The trial is the first to compare a
specific treatment. An exploratory study might also seek to identify
key issues rather
than to confirm or challenge existing results regarding the treatment
effect.
Confirmatory study: A further trial trying to confirm a
previous observation.
Sometimes a study can
have both confirmatory and exploraton
aspects. For instance, in a confirmatory trial evaluating a specific
treatment, the data can also be used to explore further hypotheses, ie,
subgroup effects that have to be confirmed by later research.
Some Other Definitions
A longitudinal study
assesses research subjects over two or more points in time; by
contrast, a cross-sectional
study assesses research subjects at one point in time or over a short period.
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