- Nitrous dioxide directly oxidizes vitamin B12, and can induce a megaloblastic anemia, and/or drop in the WBC and platelet counts. It reduces not only production, but also motility and chemotactic response of leukocytes. The ability to envelop and kill bacteria is not significantly impaired. Administration of large doses of vitamin B12 or folinic acid only partially overrides the block and rectifies bone marrow abnormalities. Vitamin B12 is a bound cofactor of methionine synthase, and, to repeat, is directly oxidized by nitrous oxide.