HYDROXOCOBALAMIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for HYDROXOCOBALAMIN (HYDROXOCOBALAMIN).
Hydroxocobalamin is a precursor of methylcobalamin and adenosylcobalamin, which are essential cofactors for methionine synthase and methylmalonyl-CoA mutase. It facilitates the conversion of homocysteine to methionine and methylmalonyl-CoA to succinyl-CoA, and neutralizes cyanide by forming cyanocobalamin.
| Metabolism | Hydroxocobalamin is converted to methylcobalamin and adenosylcobalamin intracellularly; not significantly metabolized by CYP450 enzymes. |
| Excretion | Primarily renal excretion (50-90% as unchanged drug). Biliary/fecal elimination accounts for <10%. |
| Half-life | Terminal elimination half-life: ~26-31 days. After high-dose therapy, plasma levels decline more rapidly initially (α-phase half-life ~6 hours) due to distribution, followed by slow terminal elimination reflecting tissue release. Clinically, this supports monthly dosing for deficiency correction. |
| Protein binding | ~90% bound to transcobalamin II (specific transport protein) and haptocorrin (R-protein). Binding is high affinity. |
| Volume of Distribution | Vd: ~0.1-0.2 L/kg (non-dialysis). Large apparent Vd due to extensive tissue binding (liver, kidney, bone marrow). Clinically indicates wide distribution and tissue storage. |
| Bioavailability | Intramuscular: nearly 100%. Oral: <1% due to requirement for intrinsic factor; not used for deficiency treatment. Subcutaneous: comparable to IM. Intravenous: 100%. |
| Onset of Action | Intramuscular: Clinical improvement in hematologic parameters begins within 24-48 hours; reticulocytosis peaks at 5-8 days. Subcutaneous: Similar to IM. Intravenous: Immediate but not typically used. Oral: Not applicable due to poor bioavailability. |
| Duration of Action | Duration of effect after a single IM dose: 1-2 months for hematologic response. Neurologic improvement may require 6-12 months. Maintenance therapy: every 1-3 months depending on deficiency severity. |
1000 mcg intramuscularly once daily for 1 week, then weekly for 1 month, then monthly. For maintenance: 1000 mcg intramuscularly once monthly. Route: IM.
| Dosage form | INJECTABLE |
| Renal impairment | No dose adjustment required for renal impairment. |
| Liver impairment | No dose adjustment required for hepatic impairment. |
| Pediatric use | 1-12 years: 1000 mcg intramuscularly as a single dose, followed by 1000 mcg intramuscularly once weekly for 2 weeks, then 1000 mcg intramuscularly once monthly. Infants <1 year: 1000 mcg intramuscularly as a single dose, then 500 mcg intramuscularly once monthly. |
| Geriatric use | Same as adult dosing; no specific age-related adjustment required. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for HYDROXOCOBALAMIN (HYDROXOCOBALAMIN).
| Breastfeeding | Hydroxocobalamin is excreted into breast milk in amounts sufficient to meet infant requirements. M/P ratio not established; endogenous B12 normally present. Compatible with breastfeeding; monitor infant for B12 levels if maternal deficiency. |
| Teratogenic Risk | Hydroxocobalamin is vitamin B12, essential for fetal neural tube development. No teratogenic risk at recommended doses; deficiency is associated with neural tube defects. Use in all trimesters is considered safe. |
| Fetal Monitoring |
■ FDA Black Box Warning
None.
| Serious Effects |
History of hypersensitivity to hydroxocobalamin or any component, Leber's disease (hereditary optic nerve atrophy; relative contraindication).
| Precautions | Hypersensitivity reactions (e.g., anaphylaxis), hypokalemia upon treatment of megaloblastic anemia, monitoring of potassium and reticulocyte count, interference with laboratory assays (e.g., hemoglobin, bilirubin, creatinine). |
| Food/Dietary | Alcohol consumption can reduce vitamin B12 absorption and should be limited. High doses of folic acid may mask B12 deficiency. No specific food restrictions; however, patients with pernicious anemia cannot absorb dietary B12 and require parenteral supplementation. Cyanocobalamin in food or supplements is not a substitute for hydroxocobalamin therapy. |
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| Monitor maternal serum B12, homocysteine, and methylmalonic acid levels to ensure adequate replacement. In pregnancy, monitor fetal growth and development via ultrasound if deficiency is severe or untreated. |
| Fertility Effects | No known adverse effects on fertility. Correction of B12 deficiency may improve fertility in deficient women due to role in cell division and ovulation. |
| Clinical Pearls | Hydroxocobalamin is preferred over cyanocobalamin for vitamin B12 deficiency with tobacco amblyopia or Leber's optic atrophy due to cyanide content in the latter. It is also used for cyanide poisoning (Cyanokit) at high doses, which may cause transient hypertension, reddish discoloration of skin/urine, and interference with lab tests (e.g., creatinine, bilirubin, coagulation). For pernicious anemia, lifelong intramuscular therapy is required; oral or intranasal B12 is ineffective in severe deficiency. Monitor potassium levels during initial treatment due to risk of hypokalemia from rapid erythropoiesis. |
| Patient Advice | Take hydroxocobalamin exactly as prescribed, usually by injection into a muscle. Do not skip doses, even if you feel better. · Your urine and skin may turn reddish-orange for a few days after an injection; this is harmless and temporary. · Report any signs of allergic reaction (rash, itching, swelling, severe dizziness, trouble breathing) immediately, especially after high-dose treatment for cyanide poisoning. · For pernicious anemia, you will need lifelong vitamin B12 injections. Do not stop treatment without consulting your doctor. · Avoid alcohol and limit smoking, as these can interfere with vitamin B12 absorption and utilization. · If you are pregnant or breastfeeding, inform your healthcare provider before starting treatment. |