title: Competitive inhibition of folic acid absorption in rat jejunum by triamterene.
abstract: Triamterene, a diuretic agent, has been reported to cause megaloblastic anemia in some patients. Because this drug is a pteridine derivative, we investigated its effect on folic acid absorption in the rat jejunum. In an in vivo intestinal loop method, triamterene inhibited the intestinal absorption of folic acid in a dose-dependent fashion, with 50% inhibition of systemic absorption occurring at a luminal concentration of 0.01 mmol/L of triamterene. Kinetic analysis using the influx chamber method demonstrated that triamterene is a competitive inhibitor of intestinal folate transport, with a Ki of 0.125 mmol/L. Because therapeutic doses can result in luminal concentration of the drug approximating or exceeding the Ki, the interaction between triamterene and folate absorption is potentially of clinical interest.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D005492:Folic Acid / Q000378:metabolism*; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects*; D007583:Jejunum / Q000378:metabolism; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D014223:Triamterene / Q000494:pharmacology*
chemical_list: D005492:Folic Acid; D014223:Triamterene