Possible Effects of Drugs on Vitamin Absorption or Metabolism

Ethanol Ethanol

Impairs thiamin utilization

Isoniazid Isoniazid

Interferes with niacin and pyridoxine metabolismand pyridoxine metabolism

Ethanol and oral contraceptivesEthanol and oral contraceptives

Inhibit folate absorption

Phenytoin, phenobarbital, primidone, or phenothiazines Phenytoin, phenobarbital, primidone, or phenothiazines

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

Antiseizure drugs (eg, carbamazepine, phenobarbital, phenytoin) Antiseizure drugs (eg, carbamazepine, phenobarbital, phenytoin)

Can decrease vitamin D metabolismCan decrease vitamin D metabolism

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

Interfere with absorption of vitamin B12

Oral contraceptives with a high progestin dose

Can cause depression, probably because of metabolically induced tryptophan deficiencyCan cause depression, probably because of metabolically induced tryptophan deficiency

Proton pump inhibitors

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