Drug Interaction Report

MONITOR: Coadministration of calcium channel blockers may increase the cardiovascular effects of ionic X-ray contrast media. The mechanism is unknown. A study involving 125 patients undergoing bolus contrast left ventriculography found that the hemodynamic effect of a bolus dose of an ionic agent (0.5 mL/kg of diatrizoate meglumine and diatrizoate sodium or diatrizoate meglumine and diatrizoate sodium with edetate calcium) was increased in 65 patients receiving nifedipine or diltiazem compared to 60 patients not receiving these drugs. In the patients receiving nifedipine or diltiazem in addition to ionic contrast, the hypotensive response occurred earlier (4.2 seconds versus 12.9 seconds), was more profound (maximal decrease in systolic arterial pressure was 48.5 mmHg versus 36.9 mmHg), and was more prolonged (62.3 seconds versus 36.4 seconds) than in the patients receiving ionic contrast alone. There was no difference in the hemodynamic effect of a nonionic contrast agent, iopamidol, used alone compared to nifedipine or diltiazem used in addition to iopamidol.

MANAGEMENT: Patients taking calcium channel blockers should be closely monitored for increased cardiovascular effects of ionic X-ray contrast media, such as hypotension. Use of a nonionic contrast agent, such as iopamidol, may be considered instead of ionic contrast where clinically appropriate.