Well, I got the bloodwork results back and everything that was out of whack 2 weeks ago is now normal. That makes me happy. His electrolytes and liver enzymes were both off right after the poisoning, but now all look good.
His phenobarb levels are at the high end of the range (36 out of 45). That's NOT bad, but it gives us wiggle room to bring down his dosage and hopefully elminate the ataxia (back feet dragging) while still providing some sort of safety cushion to hopefully prevent further seizures. It's not an exact science, and the neurologist wants to play it as safe as possible so I don't end up with a dog that has seizures for the rest of his life.
So ... we're going to play a bit with his meds and see how he goes for the next week. This time next week we'll decide what we're going to do for the next 6 months -- or forever. Keep your fingers crossed that all goes well for my boy.
Thanks everyone.