Hello there. My name isXXXXX and I am sorry to hear about Gus. Yes it is ok to give diphenhydramine (benadryl). The dose for dogs is much higher than it is in humans. It is 1 mg per pound. So he will need 3 tablets (75 mg) by mouth every 8 hours. I know it sounds like a high dose but again it is much higher in dogs than in humans. This should definitely help with the swelling. It will not react with the thyroid medications.
You're right--that does sound like a lot to give him, but since you say it is the proper dosage, I will give that to him.
It will definitely help him. Yes that is the published dose that is appropriate for dogs. I would repeat in 8 hours. He may get a little sleepy with the benadryl but there should not be any further side effects. Please let me know if you have any additional questions or concerns. I would be happy to help. Please do not forget to rate my response so I receive credit for my time. Thank you!
Thank you for your time. You have been very helpful. I will definitely give you a good rating for your response.