Vitamin B

# Vitamin B12 (Cobalamin) ## Overview - **Classification**: Water-soluble vitamin (B complex) - **Mechanism**: Essential coenzyme for metabolic processes, including DNA synthesis, fatty acid, and amino acid metabolism. Crucial for red blood cell formation and nervous system function. ## Primary Indications 1. **Vitamin B12 Deficiency** - Due to malabsorption (e.g., pernicious anemia, gastric bypass), dietary insufficiency (e.g., vegan). 2. **Megaloblastic Anemia** - Caused by B12 deficiency. 3. **Methylmalonic Acidemia** - Inherited metabolic disorder. ## Adult Dosing ### Standard Dosing **Vitamin B12 Deficiency (without neurological symptoms)** - **Dose**: **1,000 mcg** (1 mg) - **Frequency**: **Once daily** - **Route**: Oral - **Duration**: Chronic, often lifelong for underlying conditions. **Vitamin B12 Deficiency (with neurological symptoms / Pernicious Anemia)** - **Dose**: **1,000 mcg** (1 mg) - **Frequency**: **Daily** for 1 week, then **weekly** for 4-8 weeks, then **monthly**. - **Route**: Intramuscular (IM) or Deep Subcutaneous (SC) - **Duration**: Lifelong for chronic malabsorption. ### Dose Adjustments - **Renal Impairment**: No specific dose adjustment generally needed. - **Hepatic Impairment**: No specific dose adjustment generally needed. - **Elderly Patients**: Higher prevalence of B12 deficiency; ensure adequate intake and absorption. Oral therapy may be effective even in malabsorption with high doses. ## Pediatric Dosing ### Neonates (0-28 days) **Vitamin B12 Deficiency (congenital)** - **Dose**: **200-1,000 mcg** - **Frequency**: **Once daily** or **every other day** initially. - **Maximum**: Clinical judgment applies, typically higher initial dose. - **Special Notes**: Often IM/SC. Requires careful monitoring. ### Infants (1-12 months) **Vitamin B12 Deficiency** - **Dose**: **50-100 mcg** - **Frequency**: **Daily** for 2-4 weeks, then **weekly** or **monthly** for maintenance. - **Route**: Oral or IM/SC depending on absorption. - **Maximum**: No specific max, generally weight-based. ### Children (1-12 years) **Vitamin B12 Deficiency** - **Dose**: **100-200 mcg** - **Frequency**: **Daily** for 2-4 weeks, then **weekly** or **monthly** for maintenance. - **Route**: Oral or IM/SC depending on absorption. - **Maximum**: Up to **1,000 mcg** (1 mg) monthly for severe cases. ### Adolescents (13-18 years) - **Dose**: Generally follow **adult dosing** guidelines. - **Maximum**: **1,000 mcg** (1 mg) monthly for maintenance. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to cobalamin or cobalt. - **Relative**: Leber's disease (optic nerve atrophy) – prefer hydroxocobalamin over cyanocobalamin due to cyanide content. ### Common Adverse Effects - **Very Common (>10%)**: Generally very well tolerated. - **Common (1-10%)**: Mild diarrhea, headache, itching, injection site reaction (with IM/SC). - **Serious but Rare**: Anaphylaxis (rare), heart failure (due to fluid retention during initial treatment of severe megaloblastic anemia). ### Key Drug Interactions - **Chloramphenicol**: May reduce hematopoietic response to B12. Monitor CBC. - **Metformin**: Can decrease B12 absorption with long-term use. Monitor B12 levels. - **Proton Pump Inhibitors (PPIs) / H2 Blockers**: Can reduce B12 absorption by decreasing gastric acid. Monitor B12 with chronic use. - **Colchicine**: May impair B12 absorption. ## Monitoring & Follow-up - **Before Treatment**: Baseline B12 levels, complete blood count (CBC) with MCV, methylmalonic acid (MMA), homocysteine. - **During Treatment**: Reticulocyte count (initial response), repeat CBC and B12 levels **1-2 months after initiation**, then annually for maintenance. - **Clinical Signs**: Resolution of neurological symptoms (e.g., paresthesias), fatigue, glossitis. ## Clinical Pearls - 💡 **Oral B12** (high doses, e.g., **1,000-2,000 mcg daily**) can be effective for many forms of deficiency, even pernicious anemia, due to passive diffusion. - 💡 **IM/SC administration** is preferred for severe neurological symptoms or confirmed malabsorption where oral therapy is inadequate. - 💡 **Folate deficiency** can mask B12 deficiency; always assess both when megaloblastic anemia is present. - 💡 For patients with **Leber's disease**, **hydroxocobalamin** is generally preferred over cyanocobalamin. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.