2.5 mg once to twice daily for a “normal” sized cat. I like the generic famotidine from Walgreens. Lemme get the link…
https://www.walgreens.com/store/c/walgreens-acid-controller-tablets-original-strength/ID=300434348-product
You’re looking for the “original strength” 10 mg version. Pretty much everyone sells a generic at this strength, but the Walgreens option has tiny pills, so once you quarter them, they’re just super easy to pill or drop into food. If pilling, I like to cover with a little scrap of pill pocket (just enough to cover the pill.)
Oh, also, this pill splitter is my fav
https://a.co/d/4NF5FmT
If they need hydrolyzed, I really tend to go with Z/D. I know those rx diets aren’t exciting and they’re so costly, but it’s so much easier to take a protein reaction entirely off the table than try to muck about with various novel proteins trying to find one they tolerate when they’re super reactive. It’s so much easier to calm them down, get them to just stop reacting, and once they’re settled, you can do some novel protein trials (if you want, sometimes it’s just so much easier to stick with what works.)
Best of luck! I hope the pepcid helps!