Hi Bluegoat, finding the cause is extreemly important, is he seeing a neuro that specializes or is well respected in the neuropathy field ? as it can make a differance in some cases, i know it did for me.
There is a supplement called Benfotiamine which is a very powerfull B1, it has been known to help some people with the burning, even normal B1 taken in divided dosages [ 100mg x 3 times a day] may help some, no guaranties unfortunatly.
There are plenty of other meds besides neurotin he could try, what dosage of neurotin is he on now ? i know some neuropathies that take as much as 3,800 mg a day, you have to come down slowly off neurotin otherwise it can be very dangerous.
I tried neurotin in the begining of my PN, it did nothing for me but give me brain fog, others swear by it, meds are an individual thing.