Vitamin B12 replacement therapy: how much is enough?

Vitamin B12 deficiency becomes increasingly common with advancing age. Diverse recommendations exist for initial and maintenance therapy of deficiency states. With cyanocobalamin, the only B12 preparation available in the United States, much greater amounts of the vitamin are retained with a 1000 micrograms injection than with 100 micrograms, with no disadvantage in cost or toxicity. Maintenance therapy using the larger dosage may be necessary to meet metabolic requirements in many patients. Thus, it is recommended that parenteral regimens use 1000 micrograms cyanocobalamin: 5 or 6 biweekly injections for loading, and once-a-month for maintenance. Oral therapy with 300-1000 micrograms per day may be therapeutically equivalent to parenteral therapy.