The
quinidine levels of a number of patients have increased when
nifedipine was stopped, but no interaction has occurred in others. One study even suggests that
quinidine serum levels may be slightly raised by
nifedipine. One study with
diltiazem found that it did not interact with quinidine, whereas another found that
diltiazem increased the
quinidine AUC by 51%, with resulting significant increases in QTc and PR intervals, and a significant decrease in heart rate and diastolic blood pressure.
Monitor the outcome of concurrent use, being aware that the
quinidine dose may need to be reduced.