VI-TWEL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for VI-TWEL (VI-TWEL).
Hydroxocobalamin is converted to methylcobalamin and adenosylcobalamin, which act as cofactors for methionine synthase and methylmalonyl-CoA mutase, essential for DNA synthesis, myelin formation, and hematopoiesis. It is also a nitric oxide (NO) scavenger, reducing NO-mediated vasodilation in cyanide toxicity.
| Metabolism | Hydroxocobalamin undergoes intracellular conversion to methylcobalamin and adenosylcobalamin. It is not metabolized by CYP enzymes. Elimination is primarily via bile and urine. |
| Excretion | Primarily renal: 50-98% of a dose excreted unchanged in urine; biliary/fecal elimination accounts for <2%. |
| Half-life | Terminal elimination half-life is approximately 6 days (range 4-10 days) in patients with normal renal function; prolonged in renal impairment (up to 40 days in anuria). |
| Protein binding | Highly bound to transcobalamin II (approximately 90% bound) and other binding proteins; total plasma protein binding ~90%. |
| Volume of Distribution | 0.82-1.2 L/kg (total body water); extensive distribution into tissues, particularly liver, kidney, and bone marrow. |
| Bioavailability | Intramuscular: 100% bioavailability. Oral: 1-2% bioavailability due to limited intrinsic factor-mediated absorption; large oral doses (1 mg) allow ~1% absorption via passive diffusion. |
| Onset of Action | Parenteral (IM/SC): Reticulocyte response begins within 3-5 days; hematologic improvement noted within 7-10 days. Oral: Onset delayed and variable; not reliable for acute treatment. |
| Duration of Action | After a single IM dose, effects on erythropoiesis last 2-3 weeks; for maintenance therapy, repeat dosing every 1-3 months. Oral dosing requires daily administration. |
| Molecular Weight | 1355.38 |
1000 mcg intramuscularly once daily for 5-7 days, then 1000 mcg intramuscularly once weekly for 4 weeks, followed by 1000 mcg intramuscularly once monthly.
| Dosage form | INJECTABLE |
| Renal impairment | No dose adjustment required for renal impairment; not dialyzable. |
| Liver impairment | No specific dose adjustment guidelines; use with caution in severe hepatic impairment. |
| Pediatric use | 30-50 mcg intramuscularly once daily for 5-10 days, then 100-250 mcg intramuscularly every 2-4 weeks. |
| Geriatric use | Same as adult dosing; monitor for hypokalemia and fluid retention. |
| 1st trimester | Cyanocobalamin is generally considered safe during the first trimester at recommended doses; excessive doses should be avoided unless treating documented deficiency. No teratogenic effects have been reported. |
| 2nd trimester | Safe to use at recommended doses for treatment or prevention of vitamin B12 deficiency. Monitor levels as pregnancy increases demand. |
| 3rd trimester | Safe at recommended doses; deficiency may increase risk of neural tube defects and other complications; supplementation is advised for deficient patients. |
Clinical note
Comprehensive clinical and safety monograph for VI-TWEL (VI-TWEL).
| Placental transfer | Cyanocobalamin crosses the placenta via active transport; fetal levels are generally 50-100% of maternal levels. The transfer is necessary for fetal development. |
| Breastfeeding | Cyanocobalamin is excreted into breast milk in amounts consistent with normal B12 content. Doses up to the RDA are safe; high parenteral doses have not been studied but likely compatible. Monitor infant for adequate intake. |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to cyanocobalamin or any componentLeber's disease (hereditary optic nerve atrophy) – use hydroxocobalamin instead
| Precautions | Hypersensitivity reactions including anaphylaxis. Transient hypertension, headache, and injection site reactions. May cause reddish discoloration of urine, skin, and mucous membranes. Use caution in patients with Leber's disease (hereditary optic nerve atrophy) as cyanocobalamin may cause optic atrophy. Monitor potassium levels during treatment of megaloblastic anemia (risk of hypokalemia). |
| Food/Dietary | No known food interactions. However, alcohol can decrease B12 absorption and should be limited. Patients with low B12 should consume adequate dietary B12 (meat, fish, dairy) but cannot rely on diet alone if deficiency is due to malabsorption. |
Loading safety data…
| Lactation Rating | L1 (Safe – Compatible with breastfeeding) |
| Teratogenic Risk | First trimester: No evidence of teratogenicity in animal studies; limited human data but no increased risk of major malformations reported. Second and third trimesters: No known adverse fetal effects. Vitamin B12 is essential for fetal development and deficiency may be harmful. |
| Fetal Monitoring | Monitor maternal serum B12 levels, complete blood count, and neurological status. No specific fetal monitoring required. |
| Fertility Effects | No known adverse effects on fertility. Adequate B12 levels are necessary for normal reproductive function. |
| Clinical Pearls | VI-TWEL (cyanocobalamin) is indicated for vitamin B12 deficiency, including pernicious anemia. Monitor serum B12, homocysteine, and methylmalonic acid (MMA) levels; MMA is more specific. Intramuscular administration bypasses absorption issues in pernicious anemia. Do not use for megaloblastic anemia of unknown etiology until folate deficiency is ruled out to avoid masking folate deficiency. Watch for hypokalemia during initial treatment of severe anemia due to increased erythropoiesis. |
| Patient Advice | Take exactly as prescribed; do not miss doses. · Report any signs of allergic reaction (rash, itching, swelling) immediately. · May cause injection site pain, redness, or swelling. · Keep all follow-up appointments for blood tests. · Do not use if you have Leber's disease (optic nerve atrophy). · Inform your doctor of all medications, including multivitamins and herbal supplements. |