Vitamin B12, the largest and most complex ofall vitamins, is unique in that it contains cobalt, a metal ion. B12 deficiency may affect up to 10-15% of people over the age of 60 (Baik and Russel 1999). B12 deficiency manifests as pernicious anemia. This syndrome includes a megaloblastic anemia as well as neurologic symptoms. The neurologic manifestations result from degeneration of the lateral and posterior spinal columns and include symmetrical paresthesia with loss of proprioception and vibratory sensation, especially involving the lower extremities (Higdon 2003).
The most documented use of vitamin B12 is in the treatment of pernicious anemia. Many of the neurological, cutaneous, and thrombotic clinical manifestations have been successfully treated with oral or intramuscular cyanocobalamin (Loikili et al. 2004).
A commonly used anesthetic, nitrous oxide, inhibits both vitamin B12-dependent enzymes and may produce clinical features of deficiency such as megaloblastic anemia and neuropathy. Some experts believe that vitamin B12 deficiency should be ruled out before the use of nitrous oxide since many elderly patients will present to the operating room with deficiency (Baik and Russel 1999, Weimann 2003).
The drugs colchicines, metformin, phenformin, and zidovudine (AZT) may decrease the levels of vitamin B12 in a patient (Webb et al. 1968, Adams et al. 1983, Flippo and Holder 1993, Baum et al. 1991). Histamine-2 receptor blockers and proton pump inhibitors may decrease absorption of vitamin B12 from food, but not absorption from dietary supplements (Marcuard et al. 1994, Streeter et al. 1982, Aymard et al. 1988).
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