ABSTRACT
We hypothesized that verapamil and nifedipine would potentiate the cardiac toxicity
of magnesium in a dose-dependent manner. The hypothesis was tested in the isolated
perfused rat heart model (Langendorff's apparatus) with Sprague-Dawley rats. After
excision of hearts, each heart was exposed to increasing doses of verapamil and nifedipine
followed by magnesium sulfate. Heart rate, contractility, and left ventricular systolic
pressure were measured. Nifedipine and verapamil infusion in this model caused dose-dependent
decreases in all three parameters measured (p values 0.05 to 0.01). The addition of
magnesium sulfate potentiated these dose-dependent decreases (p values 0.01 to 0.0002).
Nifedipine and verapamil caused similar depression at equivalent doses. Nifedipine
and verapamil cause dose-dependent cardiac depression that is potentiated by the addition
of magnesium sulfate in the isolated perfused rat heart. Caution is called for when
magnesium sulfate and calcium channel blockers are administered in combination.
