Background: Magnesium sulfate (MgSO4) is the ideal drug for eclampsia prophylaxis and treatment. In China, the effective therapeutic serum magnesium level is 1.8–3.0 mmol/L. Although there have been individual reports on the use of MgSO4 in pregnant women with severe preeclampsia, there is little information on how to achieve and maintain effective therapeutic concentrations in China. This study aimed to investigate risk factors for sub-therapeutic serum concentrations of MgSO4 in patients with severe preeclampsia.
Methods: Patients with severe preeclampsia who received MgSO4 intravenous (IV) infusion were retrospectively reviewed. The maternal demographic characteristics, regimens for the administration of MgSO4, and lab test results of patients were collected. Multivariate logistic regression analysis and receiver operating characteristic (ROC) curve analysis were conducted for the risk factors influencing the serum magnesium concentration.
Results: A total of 93 patients with severe preeclampsia were included in the study. There were 41 (44.09%) patients attained therapeutic serum magnesium levels and 52 (55.91%) patients did not. A multivariate logistic regression analysis identified creatinine clearance (Ccr), whether the loading dose was given, and measurement time of serum magnesium concentration (referring to the time interval from measurement of blood magnesium concentration to the beginning of maintenance dose administration) as independent risk factors for sub-therapeutic serum magnesium concentration (P < 0.05). ROC curve analysis indicated that the continuous variable Ccr had a significant predictive value for the serum magnesium concentration, which resulted in the area under ROC curve of 0.715 and a cutoff point of 132.82 mL/min, while measurement time had limited predictive value, with the area under ROC curve of 0.650 and cutoff point of 2.375 h.
Conclusions: Ccr, whether the loading dose was given, and measurement time were independent risk factors for sub-therapeutic serum magnesium concentration. A loading dose of MgSO4 everytime before the maintenance dose, as well as an infusion time of more than 2.375 hours for MgSO4 maintenance dose are recommended for all the patients with severe PE. Routine evaluation of serum magnesium levels is a recommended practice for women with severe PE and whose Ccr is ≥ 132.82 mL/min.