Quinidine-nifedipine interaction.

Quinidine pharmacokinetics are known to be altered by a number of drugs. We present a case where dose-related increases in quinidine serum concentrations were significantly suppressed by concurrent nifedipine therapy. Clinicians should be alert to the possibility of an alteration in quinidine serum concentrations when instituting or discontinuing nifedipine in patients receiving quinidine.