Methylcobalamin, or vitamin B12, is a B-vitamin. It is found in a variety of foods such as fish, shellfish, meats, and dairy products. Although methylcobalamin and vitamin B12 are terms used interchangeably, vitamin B12 is also available as hydroxocobalamin, a less commonly prescribed drug product (see Hydroxocobalamin monograph), and methylcobalamin. Methylcobalamin is used to treat pernicious anemia and vitamin B12 deficiency, as well as to determine vitamin B12 absorption in the Schilling test. Vitamin B12 is an essential vitamin found in the foods such as meat, eggs, and dairy products. Deficiency in healthy individuals is rare; the elderly, strict vegetarians (i.e., vegan), and patients with malabsorption problems are more likely to become deficient. If vitamin B12 deficiency is not treated with a vitamin B12 supplement, then anemia, intestinal problems, and irreversible nerve damage may occur.
The most chemically complex of all the vitamins, methylcobalamin is a water-soluble, organometallic compound with a trivalent cobalt ion bound inside a corrin ring which, although similar to the porphyrin ring found in heme, chlorophyll, and cytochrome, has two of the pyrrole rings directly bonded. The central metal ion is Co (cobalt). Methylcobalamin cannot be made by plants or by animals; the only type of organisms that have the enzymes required for the synthesis of methylcobalamin are bacteria and archaea. Higher plants do not concentrate methylcobalamin from the soil, making them a poor source of the substance as compared with animal tissues.
Who should not take this medication? Patients with early hereditary optic nerve atrophy, cyanocobalmin hypersensitivity, and those who are pregnant. Your health care provider needs to know if you have any of these conditions: kidney disease; Leber’s disease; megaloblastic anemia; an unusual or allergic reaction to methylcobalamin, cobalt, other medicines, foods, dyes, or preservatives; pregnant or trying to get pregnant; breastfeeding.
Methylcobalamin is contraindicated in patients with methylcobalamin hypersensitivity or hypersensitivity to any of the medication components. Methylcobalamin is also contraindicated in patients with cobalt hypersensitivity because methylcobalamin contains cobalt. In the case of suspected cobalt hypersensitivity, an intradermal test dose should be administered because anaphylactic shock and death have followed parenteral administration of methylcobalamin.
Methylcobalamin should not be used in patients with early hereditary optic nerve atrophy (Leber’s disease). Optic nerve atrophy can worsen in patients whose methylcobalamin levels are already elevated. Hydroxocobalamin is the preferred agent in this patient population (see separate monograph in Less Common Drugs).
Most formulations of methylcobalamin injection contain benzyl alcohol as a preservative. Benzyl alcohol may cause allergic reactions. Methylcobalamin injections should be used cautiously in those patients with benzyl alcohol hypersensitivity. Methylcobalamin, vitamin B12 preparations containing benzyl alcohol should be avoided in premature neonates because benzyl alcohol has been associated with ‘gasping syndrome,’ a potentially fatal condition characterized by metabolic acidosis and CNS, respiratory, circulatory, and renal dysfunction.
Vitamin B12 deficiency can suppress the symptoms of polycythemia vera. Treatment with methylcobalamin or hydroxocobalamin may unmask this condition.
Folic Acid, vitamin B9 is not a substitute for methylcobalamin, vitamin B12 deficiency, although it may improve vitamin B12 megaloblastic anemia. However, exclusive use of folic acid in treating vitamin B12 deficient megaloblastic anemia could result in progressive and irreversible neurologic damage. Before receiving folic acid or methylcobalamin, patients should be assessed for deficiency and appropriate therapy started concurrently. The intranasal formulations are not approved to treat acute B12 deficiency; all hematologic parameters should be normal before beginning the methylcobalamin intranasal formulations. Concurrent iron-deficiency anemia and folic acid deficiency may result in a blunted or impeded response to methylcobalamin therapy.
Certain conditions may blunt or impede therapeutic response to methylcobalamin therapy. These include serious infection, uremia or renal failure, drugs with bone marrow suppression properties (e.g., chloramphenicol), or concurrent undiagnosed folic acid or iron deficiency anemia. The mechanism appears to be interference with erythropoiesis. Patients with vitamin B12 deficiency and concurrent renal or hepatic disease may require increased doses or more frequent administration of methylcobalamin.
Clinical reports have not identified differences in responses between elderly and younger patients. Generally, dose selection for elderly patients should be done with caution. Elderly patients tend to have a greater frequency of decreased hepatic, renal, or cardiac function, and also have concomitant disease or receiving other drug therapy. Start with doses at the lower end of the dosing range.
Parenteral methylcobalamin is classified as pregnancy category C. Adequate studies in humans have not been conducted; however, no maternal or fetal complications have been associated with doses that are recommended during pregnancy, and appropriate treatment should not be withheld from pregnant women with vitamin B12 responsive anemias. Conversely, pernicious anemia resulting from vitamin B12 deficiency may cause infertility or poor pregnancy outcomes. Vitamin B12 deficiency has occurred in breastfed infants of vegetarian mothers whose diets contain no animal products (e.g., eggs, dairy), even though the mothers had no symptoms of deficiency at the time. Maternal requirements for vitamin B12 increase during pregnancy. The usual daily recommended amounts of methylcobalamin, vitamin B12 either through dietary intake or supplementation should be taken during pregnancy (see Dosage).
Methylcobalamin is distributed into breast milk in amounts similar to those in maternal plasma, and distribution in breast milk allows for adequate intakes of methylcobalamin by breastfeeding infants. Adequate maternal intake is important for both the mother and infant during nursing, and maternal requirements for vitamin B12 increase during lactation. According to the manufacturer, the usual daily recommended amounts of methylcobalamin, vitamin B12 for lactating women should be taken maternally during breastfeeding (see Dosage). The American Academy of Pediatrics considers vitamin B12 to be compatible with breastfeeding. Consider the benefits of breastfeeding, the risk of potential infant drug exposure, and the risk of an untreated or inadequately treated condition. If a breastfeeding infant experiences an adverse effect related to a maternally ingested drug, healthcare providers are encouraged to report the adverse effect to the FDA.
This list may not describe all possible interactions. Give your health care provider a list of all the medicines, herbs, non-prescription drugs, or dietary supplements you use. Also tell them if you smoke, drink alcohol, or use illegal drugs. Some items may interact with your medicine.
Several drugs, including para-aminosalicylic acid, have been reported to reduce the absorption of methylcobalamin, vitamin B12. Monitor for the desired therapeutic response to vitamin B12.
The heavy consumption of ethanol for greater than 2 weeks has been reported to reduce the absorption of Methylcobalamin, vitamin B12. Patients should be aware that heavy, chronic ethanol use may counteract the therapeutic effects of vitamin B12; such patients with regular and chronic ethanol consumption be monitored for the desired therapeutic response to vitamin B12.
Several drugs, including colchicine, have been reported to reduce the absorption of methylcobalamin, vitamin B12. Colchicine has been shown to induce reversible malabsorption of vitamin B12, apparently by altering the function of ileal mucosa. Although further study of these interactions is necessary, patients receiving these agents concurrently should be monitored for the desired therapeutic response to vitamin B12.
In a study of 10 healthy male volunteers, omeprazole, in doses of 20 mg—40 mg per day, caused a significant decrease in the oral absorption of methylcobalamin, vitamin B12. Theoretically this interaction is possible with other proton pump inhibitors (PPIs), although specific clinical data are lacking. Patients receiving long-term therapy with omeprazole or other proton pump inhibitors (PPIs) should be monitored for signs of B12deficiency.
Chloramphenicol can antagonize the hematopoietic response to Methylcobalamin, vitamin B12 through interference with erythrocyte maturation. Chloramphenicol is known to cause bone marrow suppression, especially when serum concentrations exceed 25 mcg/ml. Chloramphenicol should be discontinued if anemia attributable to chloramphenicol is noted during periodic blood studies, which should be done approximately every 2 days during chloramphenicol receipt. Aplastic anemia and hypoplastic anemia are known to occur after chloramphenicol administration. Peripherally, pancytopenia is most often observed, but only 1—2 of the major cell types (erythrocytes, leukocytes, platelets) may be depressed in some cases.
Metformin may result in suboptimal oral vitamin B12 absorption by competitively blocking the calcium-dependent binding of the intrinsic factor-vitamin B12 complex to its receptor. The interaction very rarely results in a pernicious anemia that appears reversible with discontinuation of metformin or with Methylcobalamin, vitamin B12 supplementation. Certain individuals may be predisposed to this interaction. Regular measurement of hematologic parameters is recommended in all patients on chronic metformin treatment; abnormalities should be investigated.
Medications know to cause bone marrow suppression (e.g., myelosuppressive antineoplastic agents) may result in a blunted or impeded response to methylcobalamin, vitamin B12 therapy. Antineoplastics that are antimetabolites for the vitamin may induce inadequate utilization of vitamin B12. However, cancer patients usually benefit from vitamin B12 supplementation. The use of methotrexate may additionally invalidate diagnostic assays for folic acid and vitamin B12; however, this is a diagnostic laboratory test interference and not a drug interaction.
The intranasal forms of methylcobalamin, vitamin B12, should be administered at least 1 hour before or 1 hour after ingestion of hot food or liquids. Hot foods may cause nasal secretions and a resulting loss of medication or medication efficacy. Interactions between foods and oral or injectable forms of methylcobalamin are not expected.
Depressed levels of methylcobalamin, vitamin B12, and abnormal Schilling’s test have been reported in patients receiving octreotide.
The use of antiinfective agents or pyrimethamine may invalidate diagnostic assays for folic acid and vitamin B12; however, these are diagnostic laboratory test interferences and not true drug interactions.
In most cases, methylcobalamin is nontoxic, even in large doses. Adverse reactions reported following methylcobalamin administration include headache, infection, nausea/vomiting, paresthesias, and rhinitis. Adverse reactions following intramuscular (IM) injection have included anxiety, mild transient diarrhea, ataxia, nervousness, pruritus, transitory exanthema, and a feeling of swelling of the entire body. Some patients have also experienced a hypersensitivity reaction following intramuscular injection that has resulted in anaphylactic shock and death. In cases of suspected cobalt hypersensitivity, an intradermal test dose should be administered.
During the initial treatment period with methylcobalamin, pulmonary edema and congestive heart failure have reportedly occurred early in treatment with parenteral methylcobalamin. This is believed to result from the increased blood volume induced by methylcobalamin. Peripheral vascular thrombosis has also occurred. In post-marketing experience, angioedema and angioedema-like reactions were reported with parenteral methylcobalamin.
Hypokalemia and thrombocytosis could occur upon conversion of severe megaloblastic anemia to normal erythropoiesis with methylcobalamin therapy. Therefore, monitoring of the platelet count and serum potassium concentrations are recommended during therapy. Polycythemia vera has also been reported with parenteral methylcobalamin.
Diarrhea and headache.
Call your health care provider immediately if you are experiencing any signs of an allergic reaction: skin rash, itching or hives, swelling of the face, lips, or tongue, blue tint to skin, chest tightness, pain, difficulty breathing, wheezing, dizziness, red, swollen painful area on the leg.
Store dry powder at 68°F to 77°F (20°C to 25°C) and away from heat, moisture and light. Once reconstituted keep this medicine in a refrigerator between 36°F to 46°F (2°C to 8°C). Keep all medicine out of the reach of children. Throw away any unused medicine after the beyond-use date. Do not flush unused medications or pour down a sink or drain.
