Antihistamine for dogs allergy?

i had my labrador to see her vet today as her eyes are very watery and red. he took swabs and said there is no bacteria present so he was pretty certain its an allergy probably hay fever as we have been having really summery weather here in the uk this weekend. she has been given drops to use for 4-7 days. he also said that human medication can be used effectively on some dogs. piriton (chlorpheniramine) 4mg 1x2 daily and hydroxyzine (atarax\ucerax) 25mg 1x2daily. anybody have to do this for there dog? also, what are some brand names of this medication so it makes finding them easier?