FOLIC ACID Drug Interactions: What You Need to Know

INTERACTIONS Anticonvulsant action of phenytoin is antagonized by folic acid. ( 7 ) Multiple drug classes, including anticonvulsants, antibiotic/antimicrobial agents, folate antagonists, GI-binding agents, and oral contraceptives, may reduce folic acid absorption or folate levels. ( 7 )

7.1 Impact of Folic Acid on Other Drugs Folic acid may interfere with gastrointestinal absorption of methotrexate. Folic acid therapy in folate-deficient individuals may decrease serum levels of phenytoin. Folic acid may also interfere with the absorption and effectiveness of antibiotic tetracycline. Folic acid supplements are usually avoided on the day of oral methotrexate administration. Generally, the time of administration of these drugs should be separated from folic acid.

7.2 Impact of Other Drugs on Folic Acid A wide range of medications can affect folic acid levels through multiple mechanisms, including impaired absorption, accelerated metabolism, and direct inhibition of folate pathways. Enzyme-inducing anticonvulsants such as phenytoin, primidone, carbamazepine, phenobarbital, and the broader anticonvulsant class increase hepatic folate metabolism, inhibit intestinal folate-processing enzymes, raise gastrointestinal pH, or displace folate from serum proteins, collectively leading to decreased folate availability. Valproate and sulfasalazine primarily reduce intestinal folate absorption or interfere with folate-dependent metabolic pathways, while isoniazid and cycloserine reduce folate utilization through metabolic disruption. Several antifolate agents, including trimethoprim, pyrimethamine, methotrexate, and triamterene, directly inhibit dihydrofolate reductase, decreasing the formation of active folate derivatives. Additional agents such as pentamidine, antacids, cholestyramine, colestipol, and H 2 blockers impair gastrointestinal folate uptake through pH elevation, transporter inhibition, or binding of dietary folate. Nitrous oxide indirectly decreases folate activity by inactivating vitamin B12 and downstream methylation pathways, while oral contraceptives increase folate turnover and urinary loss. While on FOLIC ACID oral solution treatment, if patients are concomitantly using any of the drugs or drug classes mentioned above, then monitor for reduced efficacy and adjust the dose of FOLIC ACID oral solution as needed.

FOLIC ACID oral solution is contraindicated in patients with a history of a hypersensitivity reaction to folic acid or any of the ingredients of QUIOFIC [see Description (11) ]. FOLIC ACID oral solution is contraindicated in patients with a history of a hypersensitivity reaction to folic acid or any of the ingredients of QUIOFIC. ( 4 )

AND PRECAUTIONS Folic acid in doses above 0.1 mg daily may obscure pernicious anemia in that hematologic remission can occur while neurologic manifestations remain progressive. This may result in severe nervous system damage before the correct diagnosis is made. ( 5.1 )

5.1 Risk of Obscuring Diagnosis of Pernicious Anemia The use of single-agent FOLIC ACID oral solution (without the use of vitamin B12) is not recommended for the treatment of pernicious anemia and other megaloblastic anemias in which vitamin B 12 is deficient. Folic acid in doses above 0.1 mg daily may obscure pernicious anemia in that hematologic remission can occur while neurologic manifestations remain progressive. There is a potential danger in administering folic acid to patients with undiagnosed anemia, since folic acid may obscure the diagnosis of pernicious anemia by alleviating the hematologic manifestations of the disease while allowing the neurologic complications to progress. This may result in severe nervous system damage before the correct diagnosis is made. Adequate doses of vitamin B 12 may prevent, halt, or improve the neurologic changes caused by pernicious anemia.