Generally, cyanocobalamin or hydroxocobalamin injections are given every day for up to two weeks, followed by injections twice a week for another month. After that, injections are usually given monthly. During recovery, there is a risk of potassium deficiency as the new red cells take up the existing supply, so potassium supplements may be needed. Vitamin B12 shots must be taken for life when used to treat pernicious anemia or any other irreversible absorption problems in the intestine that are causing megaloblastic anemia. The required monthly office visits make compliance over the long term very difficult.
Some experts believe that injections every three to four months are sufficient for many patients.
To avoid an office visit, a visiting nurse or family member may be able to give the injections. A high-dose oral form of vitamin B12 is available for patients who still retain some intrinsic factor. It is widely used in Europe, but many U.S. physicians may not yet be aware of it. In Europe, a nasal spray form of hydroxocobalamin administered weekly is showing great promise for treating vitamin B12 deficiences. Treatment may not reverse neurologic symptoms if they are extensive or have continued for too long.