Amoxiicillin or clavamox, or SMZ-TMP would be good for an ear infection if you have a local vet that might prescribe those. The latter is a sulfa antibiotic. Sulmet from the feed store is the the same as sulfamethazine or SMZ. SMZ-TMP is the same as Bactrim for humans. Dawg53 has several good posts about ear infections and gunky ears.