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.