Vitamin B-12 in its usual cyano form is necessary to good colonic health. It may be injected for cats with pancreatitis and bowel problems.
In its methyl- form it can be used to help reverse Neuropathy. The more usual cyano-B12 form does not help with this.
Laurie and Jasper information and resources on using Methyl-B12 for neuropathy in felines.