Cyanocobalamin is a manufactured form of vitamin used to treat vitamin B12 deficiency. Combination drugs with pyridoxine or cyanocobalamin are also marketed. The vitamin exists in four near-identical chemical forms (vitamers)&colon; cyanocobalamin, hydroxocobalamin, adenosylcobalamin and methylcobalamin. Specific emphasis is necessary for zinc, vitamin D, thiamine, folate, cyanocobalamin, and selenium. Cyanocobalamin (a form of B12) may also be used. Multivitamins often contain cyanocobalamin, which is presumably converted to bioactive forms in the body. Animals, including humans, can convert cyanocobalamin to any one of the active vitamin compounds. Cyanocobalamin is a manufactured form with a cyano (cyanide) group bound to cobalt. Hydroxocobalamin converts cyanide to the much less toxic cyanocobalamin. Cyanocobalamin is the form in most pharmaceutical preparations because adding cyanide stabilizes the molecule. Cyanocobalamin is hygroscopic in the anhydrous form, and sparingly soluble in water (1&colon;80). Hydroxocobalamin reacts with cyanide to form cyanocobalamin, which can be safely eliminated by the kidneys. For cyanocobalamin, the R-residue is cyanide. Cyanocobalamin is commercially prepared by bacterial fermentation. Historically, the physiological form was initially thought to be cyanocobalamin.