Respiratory problem

My cat has had a sinus problem since earlier in the fall -- lots of sneezing, runny nose, etc. I took him to the vet who prescribed antibiotics. They were effective but about two weeks after completing the antibiotics, the sneezing started again. Since then we have gone throught two additional rounds of antibiotics, the latest was horrid pink stuff (Novolexin) that I could barely get down his throat! Each time the antibiotics appear to solve the problem, but after a couple of weeks the sinus problem flares up again. My cat is 15 years old and is also on thyroid meds (Methimazole), so his immune system isn't what it should be. However, he is very healthy in other respects, and when the antibiotics are working, we see his old, lively, playful self. Right now, when he's feeling poorly, he sleeps a lot and while he eats OK and seems reasonably normal, it's easy to see that he's under the weather. I'm wondering what to do next. I have heard that L-Lysine is very effective at boosting the immune system in cats with chronic upper respiratory infections, but my vet didn't endorse it. Suggestions please?

[opus88]

hi love the name!!..I was hoping someone else would give you an answer here as I'm stumped....sounds like kitty does have some underlaying immune system problem and the anitibiotics are only working temporarily.
I don't know abt the L-Lysine product...
My suggestion is you go on the ASK A VET FORUM and they can give you more help.
Or try the www.xxxxxxxx.xxx forum, I've gotten lots of answers thru that one.
I hope you get to the bottom of this must be very bothersome for kitty.
Please keep posting and let us know how kitty is doing.
there is usually alot more activity on here and perhaps a new post will get more notice...
best

[opus88]

to find the Expert Forum on Vet information
go to the right hand side of this screen and scroll down to RELATED EXPERT FORUMS...and click on geriatric pets or animal health etc...they are all hosted by a Vet.
good luck