Since it hasn't been said, I just need to add that gabapentin tastes INCREDIBLY bad. It is like, the most bitter of all the bitters. So just be aware of that. That said, I did open up my gaba capsules and put the powder into a meatball for my girl Maple for a while. She just scarfs down her meatballs so it wasn't an issue. But don't let your pups taste it.
And to reiterate: the human liquid form would be toxic to dogs because of the xylitol (which is used because it tastes to horrible otherwise). I have also read that it can be compounded into liquid form without the xylitol, but I question how easy it would go down.