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 · By Sanofi Admin

Drug Development 101: Phase 3 Clinical Trials

This post was authored by Terttu Haring, Vice President in Clinical Sciences & Operations, Global Head Trial Operations, Sanofi

If you have been following along with our Drug Development 101 blog series, you will know that we shed light on preclinical research, Phase 1 clinical trials and Phase 2 clinical trials over the course of past few months. Today, I am pleased to take the baton and share some insight into the next step in the journey from molecule to medicine – Phase 3 clinical trials.

Late-Stage & Large-Scale
Of all clinical trial phases, people are typically most familiar with Phase 3, as the results of these trials are often showcased at medical meetings and even covered by the media. Why are phase 3 clinical trials so compelling?

As discussed in the last blog of this series, only 33% of investigational drugs reach this stage of testing, so even making it to Phase 3 suggests that the investigational drug has already demonstrated some promising results in earlier research. Phase 3 is then larger in scale and longer in duration than all previous phases of clinical research, so its results provide an even more robust understanding of the investigational drug at hand, including its safety, efficacy, and ideal dosage. In fact, phase 3 trials typically include thousands of patients across the country or around the world. They can also take 1-4 years to complete. Considering all of this, Phase 3 trials can be some of the most time-consuming and challenging trials to design and execute.

That said, the larger scale and longer duration of these trials is crucial to the drug development process. It enables researchers to monitor for potential side effects over time, including any rare or long-term side effects that might have gone undetected in previous phases, which ultimately helps to ensure the drug’s safety for patients. And from an efficacy perspective, while some phase 2 trials assess the effectiveness of the investigational drug compared to a placebo, phase 3 trials confirm the efficacy of the treatment compared to other available treatment options (usually using the current standard of care).

As for the trials themselves, similar to Phase 2, they are typically randomized and double-blind, meaning study participants are picked at random to get either the standard treatment or the investigational treatment – and neither the doctor nor the patient knows which one the patient is getting. In other words, phase 3 clinical trials are essentially longer and more intensive extensions of Phases 1 and 2 that aim to definitively assess the drug’s effect on patients. Phase 3 trials are the final and most crucial phase in the drug development process before a drug can be submitted for review and approval by the U.S. Food and Drug Administration (FDA) and other health authorities in other countries. Consequently, phase 3 trials typically draw a lot of scrutiny and attention.

Next Steps
Phase 3 trials are often referred to as “pivotal studies,” which means they are intended to provide evidence about the drug for marketing approval. Once a phase 3 trial is complete, if its results are positive, the drug sponsor will typically prepare and submit a New Drug Application (NDA) to the U.S. FDA, or its equivalent in other countries around the globe, for formal review. These submissions typically include all of the data from the clinical trials that were conducted on the drug, so the agency can review it in its entirety and determine whether or not it should be approved for use.

I hope this overview of phase 3 clinical trials has given you a greater understanding of what these trials involve, how they are different from earlier phases of research, and why they are so important in the development of a new drug.

To learn more, you can also visit the FDA’s overview of the drug development process, which is available here online.


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