It boils down to three things: 1. Bacterial Infection 2. Viral Infection 3. Allergies Antibiotic was tried, it would be the top of the list. It failed. Now the Vet needs to know exactly what he is looking at, if an infection of some sort he needs to know what kind in order to treat it. It is still possible that this is a bacterial infection, an antibiotic resistant one. He still needs to know which one because there are some 'super' antibiotics that can still be used. However doctors and vets are reluctant to use these until needed simply because they are trying not to create more super-germs. Antivirals are a little tricky, one needs to know which virus you are aiming at in most cases. While they are broad spectrum antibiotics one can throw at a large chunk of bacteria with success, there really isn't a broad spectrum antiviral. Besides which, some antivirals can cause other issues and should only be used to treat when the patient has a virus. Antibiotics and Antivirals are useless against allergies. It is usually cheaper and easier to rule out infections via swap and testing, easier than ruling out allergies. So the problem all boils down to 'what ails the rabbit?' - one must have an answer for that before more treatment takes place.