Cat Allergies Treatment

I just gave my cat his first dose of this medicine, he’s been sneezing like crazy due to allergies. Has anyone had to give their cat this medicine before? Did it work for them, when did their allergies clear up?
It’s twice a day for 7 days, then once a day for 7 days, and then once every other day for two weeks. Thanks!

I have several flights booked on Southwest in the upcoming months, and now I hear they are going to permit animals on the aircraft. I was wondering how this affects other people like me.