Answer
Absorption depends substantially on intrinsic factor and gastrointestinal function, so it may be unreliable in pernicious anaemia, after gastrectomy or with malabsorption.
Sources for this answer
- Cytamen 1000mcg Injection — Current selected SmPCemc · Summary of Product Characteristics
- Cyanocobalamin 50 mcg Tablets — Current selected SmPCemc · Summary of Product Characteristics
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