Good question!
In-use usually focuses on the product remaining in a bottle, having been exposed to more oxygen and moisture due to opening (and product jostling). I haven’t heard of a blister pack in-use study as yet, but it’s not unfathomable that a regulatory inspector could raise the issue.
One response would be to explain that you do not conduct in-use for that package type with a strong justification that remaining product does not experience “exposure”.
A second response would be to design an in-use study that assumes removing the blister pack from secondary packaging represents a challenge to the product (heat/humidity/light exposure potentials?) Additionally, if there is any possibility that pulling back the lidding on one pack could inadvertently damage the seal on a connected blister, that could be a basis for observation and evaluation. Some readers may be able to share further scenarios to test.
