I am sorry to here you are worried about Ziggy. My name is Rebecca. I am a veterinarian and will do my best to help.
Has the tumor been identified, if it is cancer or not? And if it is cancer, what kind?
Has a chest Xray been taken?
Knowing the identification would help me to know if it could be related to the cough. Was it removed?
When was the Xray taken?
It is unlikely that a tumor in the throat could attach to the lungs, but it could spread or metastasize to the lungs. If there has not been a recent chest Xray, and codeine does not stop the cough, an Xray is the first thing I would do.
How much codeine is he getting, and how much does he weigh? Perhaps he needs a higher dose. Codeine is usually the strongest cough suppressant we have.
If codeine is not suppressing the cough, I would look for fluid in the lungs or tumors in the lungs; codeine would not help much with that. If there is fluid in the lungs, a diuretic may be needed to stop the coughing.
Sorry I had left for awhile when you got back to me.
The dose of codeine for a 25 kg dog would be 25 to 50 mg, every 6 to 12 hours, as needed for coughing. 5 mg may not be enough for a bad cough.
I agree about not doing invasive surgery at his age.
Let me know what other questions I can answer, and how he is doing.
You are welcome. I hope he continues to do well. Let me know if I can help with any more of your questions.