> Would the FDA say after they have given out guidance that the requirements have changed
Of course they would. They did that with MNTA by moving the goalposts wrt immunogenicity concerns which never came up during previous dialogue.
The real wild card here is that the recent heparin problems raise the bar for any potential generic entrant and MNTA may be a huge beneficiary of increased FDA caution if they can indeed satisfy the concerns (which seems likely given the recent Nature pub).