ISSN: 2424-8673
Antagonism of Vitamin B12 by Nitrous Oxide
Article Type: Review Article

Joshua R Ladner, Theodore A Alston*

Harvard Medical School, Boston, Massachusetts, USA

Corresponding Author:

Dr. Theodore A Alston

Department of Anesthesia Critical Care and Pain Medicine

Massachusetts General Hospital

55 Fruit Street, Boston, MA 02114, USA

Received: 2015-11-16 ; Accepted: 2015-12-04 ; Published: 2015-12-16
Citation: Alston TA, Ladner JR (2015) Antagonism of Vitamin B12 by Nitrous Oxide. Anethste Criti Cre 1:10445.
Copyright: © 2015 Alston TA, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cre
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Nitrous oxide (N2O) inactivates the vitamin B12-dependent enzyme methionine synthase. Despite this side effect, the anesthetic gas is generally well tolerated. However, the anti-vitamin phenomenon was originally discovered in humans and is readily demonstrable under clinical conditions.  For instance, exposure of patients to N2O routinely elevates the plasma levels of homocysteine, the precursor of methionine in the synthase reaction. Though a temporary and partial defect in methionine synthase activity is most often free of apparent harm, select patients are at risk for serious complications, such as neuropathy and problems related to impaired DNA synthesis. Plausible risk factors for toxicity include prolonged N2O exposure, concurrent methotrexate therapy and genetic deficiency of methylene-tetrahydrofolate reductase, pernicious anemia, and poor nutrition. Nutritional supplements, including folinic acid, have value in averting or palliating N2O toxicity, but their clinical reliabilities are uncertain. The only other inhaled anesthetic with anti-B12 activity is chloroform. Theoretically, deliberate inactivation of vitamin B12 merits investigation for antineoplastic and antimicrobial benefits.
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