Benadryl is safe to use in dogs, and the dose is approx. 1mg/lb every 8-12 hours; I have used 25mg twice daily in pets slightly under 20# with no ill effects. In approx 10% of dogs, any antihistamine can unexpectedly cause excessive sleepiness, or paradoxical excitment, and if these symptoms occur, then the antihistamine is discontinued. Perhaps this happened to one of the prior rescue dogs when given benadryl. Antihistamines are helpful to decrease itch in 30-40% of pollen allergic dogs, and sometimes multiple antihistamines have to be tried in order to find the most effective one for each individual dog, so if benadryl is not helping after 1-2 weeks, you can certainly try zyrtec.
Kimberly Coyner, DVM DACVD
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