He's 17 years old!!! Bless his heart and yours! Maybe you should talk to the vet. Might be time to go see God. I know it sounds heartless, but I am a firm believer in quality of life, and at 17, I know your baby has had some quality. Good luck, and God bless you.
It's always best to consult more than one vet (even at a different vet clinic) with issues as serious as this. At 17 years old (WOW! by the way), your poor baby boy definitely deserves a better quality of life, and it doesn't seem to be achievable on this particular drug. You must remember that it takes a while for a dogs system to adjust to the drug (even in a young dog) so it is difficult to say whether this is achievable in such an extremely old dog. Ask your vet.
There are other options such as a newer drug called 'Keppra' which has less side effects though is more expensive unfortunately. There is also another medication that is in a plastic syringe that you can inject slowly in his 'behind' when is having a seizure to prevent brain damage (if the seizure goes for a long time) if you don't want him on medication, though he would have to be insight 24/7 and you have to sleep sometime.
I would suggest you see an epileptic specialist if you haven't already, since vets do not know too extensively about seizures. Your dog should also have regular blood tests to check his liver since the medication can cause liver scarring.
Remember, it is very hard to find causes of seizures, and it usually requires an elimination of possibilities. A CT Scan may also be necessary to see if he has any tumors, though are extremely expensive and most of the time do not show anything if the dog is relatively healthy (eating/drinking well, healthy weight etc).
I hope this helps. I wish you both incredibly well.
Also, I heard that the pill dust should NEVER be breathed in since it can be carcinogenic! (at least in humans).
I've been reading on natural alternatives to treating seizures such as changing their diet, adding vitamin supplements and exercising etc. I've also researched other things that could possibly be causing seizures such as certain preservatives in commercial dog food etc.
Heres a great website that lets you know more: