Difference between Phase 3a vs 3b trials

Phase 3a vs 3b trials:

Here clinical trials phase 3a vs 3b explained here. Phase 3 trials are therapeutic confirmatory trials conduced in 1000-3000 patient population. After getting promising data from the Phase 2 clinical trials. Main objective of the Phase 3 trials are proving or confirming the clinical efficacy with no unacceptable safety concerns. Phase 3 trials have two sub-phases that is phase 3a and phase 3b trials.

Phase 3a trials:

With the efficacy and safety data obtained from the phase 2 trials, phase 3a trials are initiated. Studies are conducted in this phase that supports the initial claims of the sponsor to regulatory authorities. Most of the phase 3 studies are conduced in phase 3a trials like non-inferiority trials, long term safety studies and local registration studies etc.

Most of the studies producing the information supporting the patient information leaflet (PIL) / label along with post marketing commitments. Some studies may also conducted in special population depend upon the drug/disease nature.  

Most of the times drug candidate compared with an active comparator. If there is a lack of standard treatment for target disease, drug candidate compared with the placebo. This phase done before the getting the first indication approval.

Related: phase 2a and Phase 2b clinical trial differences

Phase 3b trials:

This phase starts after getting first approved indication from regulatory authority and before getting the marketing approval/ launch of the drug. While submitting the initial application to the regulatory authority, this phase studies still will go on.

These are additional studies which gather additional information like long term safety and drug effect on quality of life etc.  The intention of these studies is to produce the data supporting the publications and marketing claims. Regulatory approval authorities may rely on these phase 3b studies results before taking a decision on marketing approval of the drug even though the results are not intended for regulatory submissions.

Related: Diabetic drug classification mnemonics

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