Cocaine use shows up in some medical sites, as a toxin to nerves.
But this is not clearly explained.

http://www.examiner.com/article/what...this-condition

So figuring out what to do, is difficult to try and reverse this.
Avoiding stimulants is a first step.

Try and improve your circulation and see if that helps. Using a quality (not oxide form) magnesium supplement and soaking in epsom salt baths, may help improve blood flow.
There is a lotion too--- Morton Epsom lotion, that may help when rubbed on the tops of the feet and lower legs and ankles.
This will improve the blood flow to the feet.

If the myelin insulation of the axons of the nerves is damaged, B12 (methylcobalamin) is only one factor in helping to repair this. You need a good B-complex, like B-Right, a good magnesium and Fishoil/krill oil to help with this process. If you use statins for cholesterol, you'll have to think about stopping those, as they block remyelination.

If your PN is really from cerebral toxicity to the cocaine, and you had mini hemorrhagic strokes causing damage there, that becomes a central pain issue and is much different for pain management.

The starting dose of therapeutic use of methylcobalamin is 1mg (1000mcg) per day on an empty stomach. If testing shows you are very low in B12, 5mg a day is better to restore you more quickly. B12 does not have a toxicity profile so you can use either --stop all supplements at least a week before any testing so you don't get a falsely elevated reading.