Neurontin + Lyrica doesn't really make sense, and I don't imagine you could an insurance company to approve it. But my experience has been that the insurance companies don't expect appeals on these things, and when they get one, they grant it.

Just ask them how to appeal the denial, and proceed from there. The doctor will need to write a letter of medical necessity, for sure, but if he has a reason for what he's doing, then he has something to write.

Don't accept a denial as final without appeal.