With regard to BTD, sean007 asked Are these app

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Are these approvals grand-fathered in...or do they suffer an expiry date?

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BTD applies to a specific drug and a specific indication.
It’s granted when early clinical evidence shows substantial improvement over existing therapies for that disease or condition.

It’s not automatically permanent or “grandfathered” for all future trials.
The designation stays in effect only as long as the FDA determines the criteria continue to be met. If later data fail to confirm the early promise, the FDA can withdraw the designation.

There’s no fixed expiration date.
However, the designation typically lasts through the development program for that indication — including later-phase trials, NDA/BLA submission, and review — unless the sponsor or FDA ends it.

For subsequent trials or new indications:
If the sponsor initiates new studies for a different indication or a materially different patient population, they need to reapply for BTD.
But if new trials are part of the same indication and development program (e.g., moving from Phase 2 to Phase 3), the designation remains in effect and continues to confer its benefits — such as more intensive FDA guidance and rolling review eligibility.

Summary:
BTD doesn’t expire on a schedule, but it can be withdrawn if the data no longer support it. It’s not automatically carried over to new indications — each must qualify separately.

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