title: Drug-drug interactions: effect of quinidine on nifedipine binding to human cytochrome P450 3A4.
abstract: Quinidine is a known inhibitor of cytochrome P450-mediated nifedipine metabolism. The interactions of nifedipine and quinidine with human cytochrome P450 3A4, which metabolizes these drugs, were examined using the kinetics of CO binding to this P450 as a rapid kinetic probe of protein conformation and dynamics. This approach showed that nifedipine and quinidine bind to different P450 3A4 species, respectively termed species I and II, with distinct conformations. When both drugs were present simultaneously, nifedipine interacted with the quinidine-bound P450 species II, but not species I. These findings indicate that quinidine acts as an allosteric inhibitor by switching nifedipine binding from nifedipine-metabolizing species I to the nonmetabolizing species II.
authors.affiliation: Laboratory of Molecular Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: A P
authors.initials: AP
authors.lastname: Koley
authors.forename: R C
authors.initials: RC
authors.lastname: Robinson
authors.forename: A
authors.initials: A
authors.lastname: Markowitz
authors.forename: F K
authors.initials: FK
authors.lastname: Friedman
mesh_terms: D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000378:metabolism*; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004347:Drug Interactions; D006801:Humans; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D009543:Nifedipine / Q000378:metabolism*; D011802:Quinidine / Q000494:pharmacology*
chemical_list: D000889:Anti-Arrhythmia Agents; D002121:Calcium Channel Blockers; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; D009543:Nifedipine; D011802:Quinidine