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 · By Sanofi Admin

Drug Development 101: Phase 2 Clinical Trials

Author: Kristin Schuhwerk, VP, Global Head of Clinical Operations, Sanofi

This past November, my colleague Paul Deutsch shared some valuable information about Phase 1 clinical trials, as part of our Drug Development 101 series. Today, I’d like to build on this information by providing some insight on what comes after Phase 1 clinical trials – Phase 2.

Overall, Phase 1 and 2 clinical trials don’t usually get as much public attention as subsequent Phase 3 trials, but they are truly critical to the development of a drug. With that in mind, we thought it was important to take some time to discuss what they actually involve and why they matter.

Overarching Objective
While Phase 1 clinical trials focus primarily on assessing the safety of an investigational drug, Phase 2 trials focus more heavily on assessing its effectiveness. Specifically, as the U.S. Food and Drug Administration explains, the goal of Phase 2 is to obtain preliminary data on whether the drug works in people who have a certain disease or condition. That said, researchers also continue to assess the drug’s safety in Phase 2, including any short-term side effects that might emerge. They also continue evaluating the optimal dose of the drug.

Scope of the Studies
Phase 2 clinical trials typically involve a larger number of participants than Phase 1 trials — usually anywhere from 100-300 people, whereas Phase 1 trials usually have just 20-100 participants. Phase 2 trials also last longer. In fact, these trials can take up to two years to complete.

There are generally two types of Phase 2 trial designs. The first is a single arm trial, meaning all participants receive the investigational drug as the researchers assess the safety and its effect over time. However, more Phase 2 trials today are done as randomized trials, where one group of patients – chosen at random – receives the investigational drug, while the other group receives either a placebo or an existing treatment option (e.g., the current standard of care). This gives the researchers a point of comparison so they can assess how the investigational drug compares to either a “control” group or to another treatment that is currently on the market. To maintain the integrity of the data, these trials are also usually double-blinded, meaning participants don’t know which of these options they are actually receiving – nor do the researchers themselves!

However, Phase 2 trials typically are not large enough to show whether the investigational drug will provide long-term benefit. They do help decide if the new treatment is promising and warrants further investigation in a large-scale randomized Phase 3 clinical trial. This decision is based on the investigational drug’s effectiveness – whether it appears to be an improvement over the current standard of care or other experimental treatments and whether it provides an acceptable safety profile.

As Paul Deutsch mentioned in his Phase 1 blog post, approximately 70% of drugs in Phase 1 move on to Phase 2. Unfortunately, not as many make the leap from Phase 2 to Phase 3. In fact, only 33% of investigational drugs in Phase 2 make it past this stage of research. Therefore, demonstrating sufficient efficacy and safety in Phase 2 to qualify for Phase 3 is a significant drug development milestone!

Phase 3 is then an even longer and more rigorous step in the drug development process – one that will be discussed in our next edition of the Drug Development 101 series. Hope you’ll stay tuned!


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