It's over-the-counter, but it WORKS. It's enzyme based, with cortisone for fast healing. It's also available without the cortisone.
I used this ONCE on my Cocker after years of treating his ears, and he never had another ear problem. I also used it on a Sheltie rescue that had severe black wax, and it all came out, never to return. It IS messy, though, so try to cover the dog's head with a towel while he shakes it out. Your dog's ears will need to be washed with a mild soap when the treatment is done, it's oily.
And I agree with the poster above to reconsider what you're feeding.
Zymox - 1.25 oz - Otic Enzymatic Solution
Aids in the treatment of acute and chronic otits externa due to bacterial and yeast infections. Contains 3 active enzymes that have been shown to be antibacterial, antifungal, and antiviral.
Ingredients include natural enzymes, lysozym, lactoferrin, lactoperoxidase with 1.0% hydrocortisone.
Directions:
Apply liberally to fill ear canal. Gently massage and work into infected area. Wipe to remove excess. Treat once a days for 7 days, 14 days for chronic infections. Do not use in conjunction with other topical ear medications or ear cleaners.
Product Number: 50420
Price: $12.95
http://www.kvvet.com/KVVet/productr.asp?pf%5Fid=50420&gift=False&HSLB=False&mscssid=0089F21F519CB94C2C94EF1EB69AE68BP.S. - Read the reviews on Amazon on Zymox ear products. It's effective for nearly everyone who's tried it:
http://www.amazon.com/review/product/B0002XIYXA/ref=cm_cr_dp_all_helpful?%5Fencoding=UTF8&coliid=&showViewpoints=1&colid=&sortBy=bySubmissionDateDescending