A woman has pernicious anemia. She has been prescribed parenteral vitamin B12 tx but she is
needle phobic. Why is oral tx not preferred for this pt?
a. IM B12 is absorbed more
b. Intrinsic factor deficiency affects oral B12 utilization
c. IM B12 acts faster
d. IM B12 needs lower dosage
e. Pernicious anemia has swallowing difficulties
answer: B
B12 (cobalamin)
• binds to intrinsic factor (IF) secreted by gastric parietal cells
• absorbed in terminal ileum
• total body stores sufficient for 3-4 yr
Pathophysiology of Pernicious Anemia
• auto-antibodies produced against gastric parietal cells leading to achlorhydria and lack of
intrinsic factor secretion
• intrinsic factor is required to stabilize B12 as it passes through the bowel
• decreased intrinsic factor leads to decreased ileal absorption of B12
• may be associated with other autoimmune disorders (polyglandular endocrine insufficiency)
• F:M = 1.6:1; often >60 yr old
Treatment
• vitamin B12 1,000 μg IM monthly for life or 1,000-1,200 μg PO daily if intestinal absorption intact
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