The only times Claritin isn't recommended is if your dog has liver disease or they're on other antihistamines. (smartdogowners.com)
Dicelgis does cause drowsiness and should not be taken if you are allergic to doxylamine or pyridoxine, or to other antihistamines such as Benadryl or Dramamine. (talesofamessymom.com)
Some vets suggest using Benadryl or other antihistamine depending on the type of antivenin that will be administered. (tulsapetsmagazine.com)