Background: Magnesium sulfate is most effective for prevention and treatment of convulsions among preeclampsia women.
The therapeutic level of magnesium at 4.8 to 8.4 mg/dL and the overdose of magnesium may be fatal. In Maharat Nakhon
Ratchasima Hospital, intravenous magnesium sulfate is used with the starting dose of 4 grams followed by 1 gram per hour
for symptom control. However, between 2012 and 2013, in Maharat Nakhon Ratchasima Hospital, 14 cases of eclampsia
developed convulsions during magnesium sulfate therapy. Additionally, all of them had serum magnesium lower than the
therapeutic level and 85.7 % of them had a body weight more than the standard (Body mass index (BMI) >25 kg/m2).
Objective: To compare the success rates of yielding the standard therapeutic level of magnesium among overweight mothers with preeclampsia after receiving 1 gram and 2 gram per hour of magnesium sulfate maintenance infusion.
Material and Method: This study was a randomized controlled trial study. The 38 overweight mothers (BMI >25 kg/m2) who
were diagnosed as having preeclampsia and administered magnesium sulfate for prevention of convulsion were recruited.
The patients who had kidney impairment or were under conservative treatment were excluded. The sample size was calculated to be 19 for each group from the pilot, with five cases per group, led to type I and type II errors, 0.05 and 0.20, respectively. They were allocated with simple randomization into an experimental group that would be treated with magnesium sulfate at 2 grams per hour and a control group treated with 1 gram per hour infusion. At the fourth hour of infusion before delivery and every four hours after delivery, the magnesium levels from both groups were compared and analyzed using Chi-square.
Results: The body mass index of the experimental and the control groups were 33.5+6.84 and 33.7+6.09 kg/m2, respectively. No difference in the basic characteristics between the two groups was observed. The rate of achievement of the therapeutic level of magnesium in the experimental group was higher than that of the control group both before delivery (52.6% vs. 15.8%, respectively, RR 3.3 (95% CI 1.08-10.24)) and after delivery (84.2 % vs. 42.1%, respectively, RR 2.0, 95% CI: (1.14-3.51)). Neither the overdose of magnesium nor convulsions were found in either group. The dose of magnesium in the control group was raised to 1.5 gram per hour in four patients and 2 grams per hour in seven patients to achieve the therapeutic level after delivery.
Conclusion: The therapeutic level of magnesium in overweight mothers with preeclampsia could be more frequently accessed
before and after delivery with the dose of 2 grams per hour of magnesium sulfate infusion. No overdose of magnesium was
observed. This fact would be used to improve the guideline of preeclampsia patient care.

Keywords: Severe preeclampsia, Magnesium sulfate, Overweight