11
Phase II trials have the purpose of showing the efficacy of the new drug. The benefits
of the drug are compared against a control - either patients under placebo or
under best standard of care. The study may include patients treated at control.
But many phase II trials include no such control group, and the comparison is
only implicit by setting the standards for the judgment. These studies recruit
between 20 and 300 patients who, in contrast with phase I clinical trials, can
expect health benefits. A statistical comparison between the group of patients
receiving the new drug and the control is performed. Often the development of
a new drug fails for lack of evidence of beneficial effects in phase II. If the drug
is still promising, its safety and efficacy are tested again in a trial involving a
large number of patients in a subsequent phase III study.
Phase III trials study definitively asses the safety and efficacy of the drug. They in-
volve a large number of participants (between 300 and 3,000 or more depending
on the disease). As phase II clinical trials, they involve a comparison between a
group under the new drug and a control group. Phase III trials usually involve
randomization to treatment versus control.
Phase IV trials are also known as “post marketing surveillance trials”. Their ob-
jective is to expand the label of the drug. That is, to prove additional benefits
to its consumers or to expand the range of diseases for which the drug has a
positive effect. Moreover, phase IV trials give information about long term side
effects not detected, due to its duration, in the phase III clinical trial. They
also may be useful to analyze possible interactions with other drugs.
Phase II and III clinical trials compare the results between the treatment and
control groups. In order to establish causal conclusions between the new drug and
the results observed in the patients a random assignment of each patient to either a
treatment or a control group is important. This randomization has ethical implica-
tions related to the decision of stopping a trial. To stop a trial a balance between