DO NIFEDIPINE AND VERAPAMIL POTENTIATE THE CARDIAC TOXICITY OF MAGNESIUM-SULFATE

We hypothesized that verapamil and nifedipine would potentiate the car diac toxicity of magnesium in a dose-dependent manner. The hypothesis was tested in the isolated perfused rat heart model (Langendorff's app aratus) 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 mea sured (p values 0.05 to 0.01). The addition of magnesium sulfate poten tiated these dose-dependent decreases (p values 0.01 to 0.0002). Nifed ipine and verapamil caused similar depression at equivalent doses. Nif edipine and verapamil cause dose-dependent cardiac depression that is potentiated by the addition of magnesium sulfate in the isolated perfu sed rat heart. Caution is called for when magnesium sulfate and calciu m channel blockers are administered in combination.