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Hello. Thanks for the question.
The only safe thing that would help with pain and inflammation would be Benadryl (Diphenhydramine). The dose in dogs is 1-2 mg per lb body weight. It can be given every 6-12 hours, as needed.
They may elect to drain and tack down the cyst so that it doesn't fill back up and to make him more comfortable. That should help with his signs.
I hope this helps, let me know if you have any other questions.