Ear infection and convulsion

Question
My dog is very sick and I don't knot what else should I do, I already took him to a vet near my home but nothing is working. In less than 3 hours he had his 2 convulsion (4th of his entire life all them within these 2 months).
The local temp is 57.2F which means cold compared to a few days ago, he is a 14 years old poodle, he have osteophytosis and both back legs has shrunken, took cortisone for something like 4 years and a half. He had an ear infection and within 2 month he had 4 convulsions, 3 in less than 24hours, now sometimes he doesn't stop crying and right before he has another convulsion his breath is very wheezing and might have some spasms and fell on the floor a few times hitting his head. The vet said to cut the cortisone little by little and also prescribed pain killer and gardenal, saying that my dog have epilepsy but it looks like that its not working. His body may be a crap but the head used to be ok but now it is more like in a zombi state.
Could it be the gardenal (this is the second dose) or I lost him already? What should I do!? His vet diagnose is correct? What else could it be? Asthma? Brain aneurysm? Some sort of infection? Or I just should tell the vet to kill him? I am already accepting the idea instead of seeing him suffering this much. But if theres something that could be done, it will.

Answer
You did not indicate if the vet ran any blood tests to check for kidney function, anemia, infecton, etc.  If the dog is truly epileptic, then gardenal will have to be built up to make the brain get sedated enough not to trigger a seizure.  But I suspect that there is something else going on in this old guy.