Pearls of Wisdom: B12 Levels in Patients With Pernicious Anemia

Betty, a 66-year-old woman with pernicious anemia, has been receiving vitamin B12 injections every 1 to 3 months for the past 5 years.

She says that immediately after receiving an injection, she feels much better. At the local health-food store, a salesperson discussing B12 vitamins mentioned that oral B12 could replace her shots.

For a patient with pernicious anemia, which method of B12 administration is most effective to maintain therapeutic B12 levels?

A. B12 intramuscular injections administered every 30 days
B. B12 intramuscular injections administered every 60 days
C. Oral vitamin B12 at a 2000 µg/d dosage
D. Once-weekly vitamin B12 transdermal patch

What is the correct answer?
(Answer and discussion on next page)

Louis Kuritzky, MD, has been involved in medical education since the 1970s. Drawing upon years of clinical experience, he has crafted each year for almost 3 decades a collection of items that are often underappreciated by clinicians, yet important for patients. These “Pearls of Wisdom” often highlight studies that may not have gotten traction within the clinical community and/or may have been overlooked since their time of publishing, but warrant a second look.


Answer: Oral vitamin B12 at a 2000 µg/d dosage.

The consequences of B12 deficiency are far-reaching and have hematologic, neurologic, and orthopedic implications. Traditional thinking has asserted that because patients with pernicious anemia lack intrinsic factor (IF)—a necessary co-factor for B12 absorption—the only sensible way to treat such patients is with parenteral B12.

However, we may have overlooked the fact that although IF enhances B12 absorption, if enough B12 is given orally, B12 deficiency can be satisfactorily managed.

B12: Parenteral or Other?

B12 Parenteral

The Research

In one study, participants who received 2000 µg/d of B12 orally had superior plasma B12 levels compared with individuals who received 1000 µg of B12 via intramuscular injection given as 9 doses over 90 days.

Oral B12 Without IF: The Evidence

Oral B12

Note: There are also transnasal gel versions of B12 available—applied weekly in 1 nostril—that have similarly favorable outcomes.

What’s the “Take Home”?

Early in my career, I encountered many older patients who believed that B12 injections were a general panacea. In the face of legitimate B12 deficiency, oral, nasal, or parenteral therapies are all efficacious—the emphasis should be placed on patient preference.


1. Elia M. Oral or parenteral therapy for B12 deficiency. Lancet. 1998;352(9142):1721-1722.

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