Male Rat excess chest movement

Question
Hi Debbie,
One of my male rats, Little Bean is having some problems and I hope you can help. I have first read again your Rat Guide in case I missed something that may help. He is 31 months old, unneutered and very big and fat at 860g. He is on a combination treatment of Marbocyl (similar to Baytril) and Doxycycline and has been for the last 5 months.
His chest has started moving quite excessively and his head is also going up and down, difficulty breathing I guess. Also this morning a bit of puffed out fur too. I have tried him on Enalapril but saw no improvement after 6 days SID, so stopped.
Can you give me any other suggestions on what this could be caused by and how to treat it if possible. Should I try him on Amoxicyline maybe?
Thank you so much for any help.
Dawn

Answer
Hi Dawn,
Yes, I recommend putting him on amoxicillin as he might have a secondary infection that the Marybocyl and doxy can't work on. Since he is almost 2 lbs, you want to give him at least 20 mg twice a day. I hope it helps. If it doesn't, the next 2 drugs to try would be a bronchodilator, or prednisone for inflammation in his lungs.
Deb