Don't dose him unless you have to. To help you can give them locally sourced raw honey as it can help build the immune system to allergens in your area, probiotics, a good doggie suppliment like NuVet or Hardy Pet, plain yogurt or kefir as well as they all help to build a healthy immune system. As for medications it is 1mg per pound for Benedryl. For Claritin or Zertec it is generally 1 pill per day if needed. Do not use the "D" versions of any of them as the decongestant can harm your pup.