Objective: To determine the effect of maternal body weight (BW) to the serum level of Magnesium sulfate (MgSO₄) in preeclampsia and define the optimum maintenance doses in different maternal weight groups.

Materials and Methods: A cross sectional study of preeclampsia patients who were treated by MgSO₄. The percentages of subtherapeutic level of Mg in the first four hours and the optimum maintenance dosage, which achieved the therapeutic level, were compared in different BW groups.

Results: Four hundred seventy patients were included in this study. According to BW, 45.6% of the group with BW of less than 60 kg achieved therapeutic level in the first four hours, compared with 23.8% of the group with BW 60 to 79.9 kg, 14.9% of the group with BW 80 to 99.9 kg, and 0% of the group with BW of 100 kg or more (p<0.05). After adjusting the maintenance dose of MgSO₄, the optimum maintenance dosages were 1.11±0.19 g/hour in BW of less than 60 kg group, 1.28±0.34 g/hour in 60 to 79.9 kg group, 1.35±0.39 g/hour in 80 to 99.9 kg group, and 1.43±0.44 g/hour in 100 kg or more group (p<0.05).

Conclusion: The higher maternal BW causes the lower serum Mg level in preeclamptic patients who were treated with MgSO₄. From the present study, the optimum maintenance dose was suggested for each weight group. However, the effectiveness of this protocol needs further evaluation.

Keywords: Preeclampsia, Eclampsia, Pharmacology, Labor management, Magnesium sulfate