Folic acid drug interactions

Folding paperboard food cartons, 25 36 Folex, 13 43t, 52-53 Folic acid, 2 822 27 655 25 800-803 ascorbic acid and, 25 769 cofactor forms of, 25 801-802 dietary sources of, 25 803 drug-nutrient interactions involving, 25 802-803... 

Drugs that may interact with folic acid include aminosalicylic acid, oral contraceptives, dihydrofolate reductase inhibitors (eg, methotrexate, trimethoprim), sulfasalazine, hydantoins. 

Drug/Lab test interactions Methotrexate, pyrimethamine, and most antibiotics invalidate folic acid and vitamin Bi2diagnostic microbiological blood assays. 

Drugs that may interact with sulfasalazine include digoxin, sulfonylureas, folic acid, cyclosporine, methotrexate, thiopurines, and warfarin. 

For a displacement interaction to become clinically important, a second mechanism usually operates sodium valproate can cause phenytoin toxicity because it both displaces phenytoin from its binding site on plasma albumin and inhibits its metabolism. Similarly aspirin and probenecid (and possibly other nonsteroidal anti-inflammatory drugs) displace the folic acid antagonist methotrexate from its protein-binding site and reduce its rate of active secretion by the renal tubules the result is serious methotrexate toxicity. 

Most interactions of trimethoprim and co-trimoxazole with other drugs are due to fohc acid antagonism. This may be more pronounced with co-trimoxazole than with either drug alone. Such interactions have previously been suspected with anticonvulsants, such as barbiturates, phe-nytoin, and primidone, which themselves produce folic acid deficiency and megaloblastic anemia (88). In order to circumvent the risk of folate deficiency, folic acid or folinic acid can be given. There is some concern that folate replacement may antagonize the desired antimicrobial effect, particularly in some protozoal parasites, but this concern has been debated (89). 

A complex interaction of phenytoin with folic acid also has been described, making vitamin ingestion an important part of the drug history. Phenytoin reportedly decreases fohc acid absorption, but folic acid enhances the clearance of phenytoin. Replacement of folic acid can reduce phenytoin concentrations and result in loss of efficacy. ... 

Toxicity The toxic effects of sulfonamides include skin rashes, gastrointestinal distress, hemolysis, kidney damage, and drug interactions caused by competition for plasma protein binding sites. Pyrimethamine may cause folic acid deficiency when used in high doses. 

Berg MJ, Fischer LJ, Rivey MP, Vem BA, Lantz RK, Schottelius DD. Phenytoin and folic acid interaction a preliminaiy report Ther Drug Monit (19S3) 5,389-94. 

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