Adults

For pernicious anemia, initially 250 mcg to 1000 mcg daily or every other day for 1-2 weeks, followed by 250 mcg to 1000 mcg monthly for maintenance. Dosage may vary based on the severity of deficiency and individual response.

Elderly

Similar to adult dosage; however, renal function should be considered. Lower initial doses may be appropriate.

Renal_impairment

No specific dose adjustment is generally required, but close monitoring of B12 levels and clinical response is recommended.

Onset

Hematological response (e.g., reticulocytosis) typically observed within 3-5 days. Neurological improvements may take weeks to months, and some damage might be irreversible.

Excretion

Mainly excreted via the kidneys (urine), with a small amount excreted in bile.

Half life

Circulating half-life is approximately 6 days. Total body stores can last for several years.

Absorption

Rapidly and completely absorbed after intramuscular or deep subcutaneous injection, bypassing the need for intrinsic factor.

Metabolism

Converted to active coenzymes (methylcobalamin and adenosylcobalamin) in the liver and other tissues. Stored primarily in the liver.

Folic acid

Large doses of folic acid may mask Vitamin B12 deficiency symptoms, particularly neurological manifestations.

Chloramphenicol

May decrease the hematologic response to Vitamin B12, especially in patients with megaloblastic anemia. Monitor CBC.

Colchicine, Neomycin, Aminosalicylic acid, Omeprazole, Metformin, H2-receptor blockers

May reduce the absorption of oral Vitamin B12, but this is less relevant for injectable forms.