Drugs that increase the requirements for pyridoxine include hydralazine, isoniazid, penicillamine and oral contraceptives, neomycin, aminosalicylic acid, histamine H2-antagonists and colchicine may reduce the absorption of vitamin B12 from the gastrointestinal tract. Oral contraceptives may reduce serum concentrations of vitamin B12. Though unlikely to be of clinical significance, many interactions of vitamin B12 should be taken into account when performing assays for blood concentration.
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