CARDIOVASCULAR CONSEQUENCES OF THE CONCOMITANT ADMINISTRATION OF NIFEDIPINE AND MAGNESIUM-SULFATE IN PIGS

There is concern regarding the interaction of magnesium sulfate and ni fedipine used concomitantly in obstetrical patients, because both are calcium channel antagonists and may induce myocardial depression as we ll as peripheral vasodilatation. The objective of this study was to de termine the hemodynamic consequences of concomitant administration of nifedipine and magnesium sulfate in anesthetized pigs. Twelve pigs wer e anesthetized with sodium pentobarbital, intubated and mechanically v entilated. Following placement of invasive monitors, baseline hemodyna mic measurements were made. Animals were randomized to one of two grou ps. Group I received nifedipine first, and then magnesium sulfate. Gro up II received magnesium sulfate first, and then nifedipine. Hemodynam ic measurements were recorded. Hypotension was treated with calcium ch loride, ephedrine and phenylephrine. Nifedipine alone (Group I) decrea sed peripheral vascular resistance and mean arterial pressure (MAP) (P < 0.05). Magnesium sulfate alone in group II decreased the first deri vative of left ventricular pressure (LVdP/dt) and increased left ventr icular end-diastolic pressure (LVEDP) (P < 0.05). Magnesium sulfate al so decreased peripheral vascular resistance and MAP. The concomitant a dministration of nifedipine and magnesium sulfate in both groups I and II led to a further decrease in myocardial contractility, as evidence d by a decrease in LVdP/dt and increase in LVEDP (P < 0.05). Treatment with calcium chloride or ephedrine was only partially successful in i mproving myocardial contractility. Phenylephrine increased peripheral vascular resistance and MAP, but did not improve myocardial function. In conclusion, the depressive effects of nifedipine and magnesium sulf ate on the cardiovascular system are potentiated when administered con comitantly.