Vitamin B 12 (Cyanocobalamin)

Incidence of deficiency in USA varies with age: 5% of those <55 y, 10% of those 55–64 y, 10–15% of those 65–74 y, and 24% of those 74–80 y old. Some 75% of those >64 y with vitamin B ₁₂ deficiency do not have anemia or even RBC abnormality. CDC states that 1 in 31 individuals 51 y of age or older are deficient in B ₁₂ .

Prescribed for pernicious anemia and demyelinating CNS disease.

Lack of gastric secretion of intrinsic factor leads to malabsorption of vitamin B ₁₂ ; therefore IM route preferred. Recent studies have documented that high-dose oral replacement is effective. Strict vegetarian diet–induced deficiency state responds to oral supplementation.

Until a person reaches midlife, he or she probably gets all the B ₁₂ needed from food (unless vegetarian). Autoimmune achlorhydric gastritis (pernicious anemia) decreases absorption because of loss of intrinsic factor. Pts are also almost certainly low on B ₁₂ if they have been taking a proton pump inhibitor for a long time, which seriously diminishes B ₁₂ absorption. B ₁₂ absorption also generally decreases with older age.

Also associated with Helicobacter pylori infection, chronic alcohol ingestion, long-term metformin administration, and pancreatic exocrine deficiency conditions.

Permanent neurologic injury, classic combined system disease with paresthesias, balance problems with loss of position and vibratory sense, and lack of myelination in long tracts; preventable with recognition and cobalamin replacement.

Interactions and neurologic injury with folate, methionine synthetase inhibitors, and nitrous oxide, which can produce rapid neurologic deterioration.

Hyperhomocysteinemia, which causes thrombophilia and vascular disease, associated with adequate folate and B ₁₂ deficiency.