purulent nasal discharge from one nasal passage

My 15 year old doxie sneezes several times a day and each time has thick yellow discharge from one side of nose. I took him to the vet in November 2009, lungs were clear, nothing trapped in nostril, no eye discharge.  The vet said it did not appear he had an infection but treated him with antibiotics and ear drops.  He still is sneezing daily with the thick discharge.  

Any suggestions will greatly be appreciated.

CF

[Kimberly Coyner, D.V.M., DACVD]

Yellow discharge from the nose can be due to a nasal problem (fungal or bacterial infection, foreign body such as a piece of grass, nasal tumor), or to a draining toothroot abcess (abscess). Since the problem has persisted despite antibiotic treatment, further evaluation of the nose, sinuses and toothroots with xrays +/- CT scan is indicated. If xrays demonstrate a toothroot abcess (abscess), then extraction of the affected teeth would be needed. If a mass is found in the nose on xrays, then biopsy would be the next step.
Good luck,
Kimberly Coyner, DVM DACVD