Trial Phases for Investigating Drugs and Treatments

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In this Section

Main Article

FDA-Approved Medications

Experimental Medications

New Directions in MS Research

Closing Notes


Trial Phases for Investigating Drugs and Treatments

Every approved treatment for MS has undergone extensive study prior to receiving approval by the United States Food and Drug Administration (FDA). The process of testing a new drug therapy for MS is time-consuming, and all drugs must undergo several phases of investigation in order to be deemed both safe and effective.

Phase I: Phase I studies are primarily concerned with assessing the drug’s safety. This initial phase of testing in humans is done in a small number of healthy volunteers, and is designed to determine what happens to the drug in the human body – how it is absorbed, metabolized, and excreted.

Phase I trials are referred to as “open label” and “unblinded,” because everyone – the patient, medical staff, and investigators – knows the drug and dose that each participant is receiving. A Phase I study will investigate side effects that occur as dosage levels are increased. Phase I trials can take several months to one year to complete.

Phase II: Once a drug has been shown to be safe, it must be tested for efficacy. This second phase of testing may last from several months to two years, and involve up to several hundred patients. Phase II studies are often “double-blinded,” meaning that the participants, medical staff, and investigators are not told who is receiving the drug and who is receiving the placebo.

These studies are also “randomized,” so that participants are assigned to treatment groups (or “treatment arms”) based on chance. One group of patients receives the experimental drug, while a second “control” group will receive a standard treatment or placebo. In this manner, the study can provide the pharmaceutical company and the FDA information about the relative safety of the new drug, and its effectiveness. Only about one-third of experimental drugs successfully complete both Phase I and Phase II studies.

Editor’s note: Initial study results from therapeutic agents under investigation should be considered as preliminary, since additional studies and/or evaluations may be needed to prove the safety and efficacy of these agents. MSAA does not endorse or recommend any specific products or therapies. Readers are advised to consult their physician before making any changes to their medication, diet, exercise, or other treatment regimen.

Phase III: In a Phase III study, a drug is usually tested in several hundred to several thousand patients, usually in multiple medical facilities around the world. Phase III studies typically last several years. This large-scale testing provides the pharmaceutical company and the FDA with a more thorough understanding of the drug’s effectiveness, benefits, and the range of possible adverse reactions.

Most Phase III studies are randomized and blinded trials. Only after a Phase III study is successfully completed can a pharmaceutical company request FDA approval for marketing the drug.

Phase IV: Phase IV clinical trials are conducted after a drug has been approved. Participants are enrolled to further monitor safety and side effects, while evaluating long-term efficacy.