ObjectiveTo describe the relationship between plasma magnesium (Mg2+) concentration and blood pressure response in pregnant women with preeclampsia.MethodsFifty-one preeclamptic women were studied after receiving two consecutive magnesium sulfate infusions (120 mg/kg for 1 hour and 24 mg/kg for 5 hours). Mg2+concentration and systolic/diastolic blood pressure were measured at 0, 0.5, 1, 2, 4, 6, 7, 9, 11, 13 and 15 hours after the beginning of the first infusion. A population pharmacokinetic-pharmacodynamic model was fitted to the data with the computer program NONMEM.ResultsPharmacokinetics were described by a two-compartment model. Population parameter estimates were 5.0 L/h for body clearance (CL), 24L for central volume (Vc), 25L for peripheral volume (Vp) and 5.6 L/h for intercompartment clearance (Q). The interindividual variability in CL, Vc, Vpand Q was 39, 26, 38 and 59%, respectively. The mean population estimates for systolic (diastolic) blood pressure were 36.8 (27.8) mm Hg for the maximum decrease (Emax), 0.75 (0.88) mmol/L for the Mg2+concentration (above baseline) eliciting half-maximum effect (EC50) and 0.76 (0.5) h−1for the equilibrium rate (keo) of the effect compartment model.ConclusionMg2+concentrations within the range (2−4 mmol/L) proposed for treatment of preeclampsia produce greater than half-maximal lowering of systolic and diastolic blood pressure.