Possible Effects of Medications on Vitamin Absorption or Metabolism

Ethanol

Impairs thiamin utilization

Isoniazid

Interferes with niacin and pyridoxine metabolism

Ethanol and oral contraceptives

Inhibit folate absorption

Phenytoin, phenobarbital, primidone, or phenothiazines

In most patients, cause folate (folic acid) deficiency*, probably because hepatic microsomal drug-metabolizing enzymes are affected

Antiseizure drugs (eg, carbamazepine, phenobarbital, phenytoin)

Can decrease vitamin D metabolism

Aminosalicylic acid, slow-release potassium iodide, colchicine, trifluoperazine, metformin, ethanol, and oral contraceptives

Interfere with absorption of vitamin B12

Proton pump inhibitors

Can decrease absorption of vitamin B12, vitamin C, iron, calcium, and magnesium