Not a vet, and have never used it in my own animals, but I am a diabetic, so please use pure glucose with caution. An energy boost is one thing, but once the glucose hits the blood, the body tries to take excess away, and you can easily end up with a *low* following the *high*, which won't do your little man any good. Little and often - allow the body to take it and use it, and not overload it with sugar it feels it needs to deal with. If a diabetic has low sugar, the advice is to give jam sandwiches - jam for the initial sugar boost, bread for the longer acting carbohydrate boost. Not a mars bar, much as I would like it to be ! At the vet practice I work at, we give *poor doers* a mix of glucose solution with black treacle/mollases, rubbed on gums every hour or so, and drizzled on forage ( ivy, willow, hay etc ) so they are taking in small amounts over a longer period of time - can make a mix/pellet more palatable too.
Good luck with your boy, I hope he feels better soon, and recovers well.