Vitamin B12 Deficiency


In conditions in which there is a risk of developing vitamin B12 deficiency (e.g., total gastrectomy, ileal resection), prophylactic vitamin B12 should be prescribed.

Active Treatment

Once the diagnosis has been accurately determined, several daily doses of 25-100 |g may be used to initiate therapy as well as potassium supplements.* Alternatively, in view of the ability of the body to store vitamin B12 for long periods, maintenance therapy can be started with monthly intramuscular injections in doses between 200 and 1000 |g. Most cases of vitamin B12 deficiency require treatment throughout life.

Patients with defects affecting the intestinal absorption of vitamin B12 (abnormalities of IF or of ileal uptake) will respond to parenteral B12. This bypasses the defective step completely.

Patients with complete TC II deficiency respond only to large amounts of vitamin B12 and the serum cobalamin level must be kept very high. Doses of 1000 | g IM two or three times weekly are required to maintain adequate control.

Patients with methylmalonic aciduria with defects in the synthesis of cobalamin coenzymes are likely to benefit from massive doses of vitamin B12. These children

*Hypokalemia has been observed during B12 initiation treatment in adults.

may require 1-2 mg vitamin B12 parenterally daily. However, not all patients in this group benefit from administration of vitamin B12.

It may be possible to treat vitamin B12-responsive patients in utero. Congenital methylmalonic aciduria has been diagnosed in utero by measurements of methyl-malonate in amniotic fluid or maternal urine.

In vitamin B12-responsive megaloblastic anemia, the reticulocytes begin to increase on the 3rd or 4th day, rise to a maximum on the 6th to 8th day, and fall gradually to normal by about the 20th day. The height of the reticulocyte count is inversely proportional to the degree of anemia. Beginning bone marrow reversal from mega-loblastic to normoblastic cells is obvious within 6 hours and is complete in 72 hours. Neurologically, the level of alertness and responsiveness improves within 48 hours and developmental delays may catch up in several months in young infants. Permanent neurologic sequelae often occur. Prompt hematologic responses are also obtained with the use of oral folic acid, but it is contraindicated because it has no effect on neurologic manifestations and may precipitate or accelerate their development.

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