well, you cant compare bac water to the solutions they use for the pens.I dont think it is degrading that fast (within 2 weeks). If we look at most Injection-pens with semaglutide, Liraglutide or Dulaglutide they usually come in a up to 4 weeks ready to use sized pen. So I believe if reconstituted with bac water it should be good to go for at least 4 weeks in the fridge. Im just guessing in the dark but that would make sense.