"B12 Shots"—Still Another Side of the Coin

To the Editor.—  In his article "'B₁₂ Shots': Flip Side" (231:289, 1975) McCurdy states: "My first article emphasized that most cyanocobalamin injections have little justification, although they may sometimes have a placebo effect. The flip side of this coin: when cyanocobalamin therapy is needed, it is really needed and needed permanently."To continue the metaphor, a three-sided coin would be needed, since, whether the cyanocobalamin shot is therapeutic or acts as a placebo, there is always the possibility of an allergic reaction.I have described such a reaction¹ in a 63-year-old woman who noted that following each injection of cyanocobalamin the area of injection had become red, tender, and pruritic. Oral ingestion of cyanocobalamin produced similar flares in the sites of previous injections. This patient had positive patch reactions to a 2% aqueous solution of cobalt chloride and to cyanocobalamin solutions in the strengths of 100μg and 1,000μg/