Benadryl usually does not work well for allergies in dogs, and you do have to give it every 4-6 hrs for it to even potentially be therapeutic anyway, which is not convenient. For OTC meds, Vet Derms recommend Claritin or Zyrtec, which are 24 hr meds. But there are prescription meds for allergies that work much better.
For how to deal w/ allergies, read this:
http://www.yorkietalk.com/forums/die...tart-here.html