Never needed the mouthwash. I used coconut oil, some of which may have been infused with Aunty Margs herbal remedy, in the evening which seemed to stop my mouth drying out. It also, I think, helped with my bowels which remained fairly regular, but terribly painful, in the couple of days post treatment.
I don't know if BMO prescribe antihistamines along with Neulasta, they never used to. Neulasta boosts your white cell production and can feel like a total body toothache when it kicks in about day 4 after treatment. If Ms. C, whom i presume is your onc, pooh-pooh's the idea of claratyne ask her if she has any objection to you taking it anyway.