Pharmacokinetics of magnesium sulfate in the sheep model.

The pharmacokinetic parameters of MgSO4 were followed in the pregnant sheep model following intravenous dosages of MgSO4 comparable to those used in the therapy of the preeclamptic woman. Hemodynamic parameters, including maternal arterial pressure, central venous pressure, systemic vascular resistance, pulmonary artery pressure, heart rate, cardiac output, cardiac index, rate pressure product, stroke volume, stroke index, blood gases, fetal arterial pressure, heart rate, and blood gases, all remain stable during the infusion of MgSO4. Biochemical changes accompanying MgSO4 infusion in these doses were evaluated. It was found that the fetal serum levels of MgSO4 were approximately 70% of those in the mother. The MgSO4 was rapidly excreted into the maternal urine and 8.9% of the MgSO4 infused was cleared by 2 hr after the termination of the infusion. MgSO4 was also excreted by the fetus into amniotic fluid. It was found that a minimum dosage of 1 mg/kg/hr of magnesium was required to achieve a magnesium level in maternal serum at the lower limit of the therapeutic range of 4 mEq/L.