http://benadrylfordogs.info/benadryl-dosage-for-dogs/. Benadryl which is also referred to as diphenhydramine is a medication which is readily available over the counter and is used to treat allergic reactions in both humans and animals especially dogs.This medication is FDA approved and is therefore quite safe for use.enadryl Dosage for Dogs: The right dosage of this medication is usually determined in two different ways as indicated below: It is administered by giving 1 milligram for every pound of a dog s weight after every 8 hours or three times per day.