You may want to talk with your vet about a better course of treatment. Sulfanomides (SMZ is one of these) is one of those old school drugs that are notvery effective these days with all of the resistant bacteria. I haven't used (or know of any exotic focus vets still use) this family of drugs in years. It can also be devastating to the beneficial bacteria in the GI. Fenbendazole (Panacur) is the long time "standard" treatment for E Cuniculi. Couple of things here....first, as I previously mentioned, it's not the EC causing the tilt....if EC is involved, the tilt is caused by opportunistic bacteria allowed to grow due to a compromised immune system. And it would be compromised by the EC. While Fenbendazole has been the standard for treatment....fact is that the parasite is in the brain and Fenbendazole has a difficult time penetrating the blood/brain barrier so it can easily reach the parasite. The initial presentation of an active EC infection are a paresis in the hind quarter (most often the left rear leg) and some degree of urinary contenance. Most vets have never actually seen a full blown case of EC. There is a test, called a titer, that can check for antibodies for EC....but nearly all domestic rabbits will titer positive since they have been exposed....a titer is used as part of the diagnosis along with clinical presentations.
Most of the time, the bacteria causing head tilt is some strain of pasteurella. But we have seen other bacteria (and even yeast) causing tilt. I don't like using the term "stronger" antibiotics because that wouldn't be technically correct, but in most cases, a more aggressive and targeted antibiotic is necessary....and sulfa isn't usually up to the task. In the case of most ear infections, drugs such as Zeniquin, Penicillin, Convenia or Chloramphenicol would be much better choices. Pain meds should be implemented. Keeping the eyes hydrated would be beneficial. While the Fenbendazole probably won't help if it's EC, it is beneficial in ridding the GI of general worms. Bene Bac is good to use in order to help stabilize the pH in the GI.
This type of situation has to be treated aggressively if there is to be hope of a favorable resolution and correction of the tilt.
Randy