When I read your post today, I was very surprised that your doctor has you on morphine 2x a day. As Gerry said, 12 hours is a long time for morphine to remain effective. It is usually taken 3x a day, some doctors will even go 4x a day. Perhaps it is because you are also taking Oxycodone as well, I do not know.

Methadone is a very scary prescription. There are so many side effects that could potentially be life threatening. It does work on the NMDA receptors, but there are others that do as well... Tramadol, Nucynta, Dextromethorphan, and Ketamine. I am sure that there are plenty of others. Those are just the ones I know of.

I know very little about SFN. I do not know if your doctor wants to use Methadone because it is an NMDA receptor blocker or other reasons, it is just my best guess.

Sending healing hugs and thoughts. I hope that you are able to find the relief you are expecting with the increase in morphine.