Given I'm not a Vet, I'm not sure if I should mention this...

But, Benadryl (for humans) is also given to our guys as well.
I had a conciliation with my Vet, and he told me to just buy it over the counter.
I had to half the 25mg tabs, to accommodate the weight of the animal.
So, if it's any value, that was 12.5mg per 10 lbs. (all my guys are pretty hefty)

You might just call your Vet and ask if it's ok, and how much (mg) for your guys.
Anyhow, it does the trick when my guys get sneezy.