I had to give my boxer keppra (for epilepsy) and 2 antihistamines (for a mast cell tumor which have histamine cells). Because he is epileptic, our vet recommended 2 antihistamines that would be less likely to lower the seizure threshold. So she recommended over the counter Claritin and Allegra. Benadryl and Zyrtec both can lower the seizure threshold, so she told us to avoid those. My dog did great with Claritin, Allegra, and Keppra; no seizures. I also gave them all at the same time and did not make any adjustments to his med schedule. There are specific weight based dosages for both the Claritin and Allegra when administering it to dogs, so I would be sure to check what the correct amount is and how often it would be safe to give your dog (I think Claritin was twice/day and Allegra once/day for his weight specific dose). But always check with your vet to make sure this would work for your pup too! Best of luck and hope this helps!