Ok, is the circling always to one direction? Counter clockwise vs clockwise?
Ok good that you started the drops AFTER the signs. Some medications will cause ototoxicity, inner ear
toxicosis if the ear drum is not intact. Those tend to resolve when the medications are stopped.
If the circling is one direction, it might relate to the side of the head that the lesion is located on. A clockwise direction is usually going to be right ear related for example.
The thing with vestibular disease is there is not a really good treatment for it. Steroids and antibiotics are used but may not really do much. Supportive care is important. Fluids and IV might be necessary for patients that will not eat, or can't eat. I have recently started using a medication called Cerenia on these patients.
Cerenia blocks nausea at the level of the brain
. And, I think that it keeps these patients with inner ear, or vestibular disease from getting dizzy. They recover faster and are able to eat sooner.
If it is vestibular disease, most dogs repond in about 3-5 days. Some are never quite normal again. I don't think they really heal, I think they just get used to the changes and adapt.
The direction of the eye movement may be a very good thing. Fast twitch in one direction only can be an indication of a brain tumor. Typically, the slow drift will be toward the tumor side. The fast phase is away from the tumor. So, if the circling is to the right, and the slow phase is to the right, I would suspect a likely right sided lesion.
Best is to keep the pet calm and safe - away from stairs, etc - for the next several days. be sure that he is eating. If not, he will need hospitalization for fluid treatment, and electrolytes.