A retrospective review of on-admission factors on attainment of therapeutic serum concentrations of magnesium sulfate in women treated for a diagnosis of preeclampsia

Introduction: There is little information on the effect of maternal characteristics and on-admission laboratory parameters to the therapeutic serum magnesium sulfate (MgSO₄) levels in women with preeclampsia (PE). We sought to identify factors that may predict timely attainment of therapeutic serum magnesium levels after intravenous administration for seizure prophylaxis. Materials and methods: On-admission factors of 360 women with PE who received intravenous MgSO₄ (4-g loading and 2-g/h maintenance) for seizure prophylaxis were retrospectively reviewed. Parameters of those who attained therapeutic serum concentrations (4.8–8.4 mg/dL) within 2 h (Group A) and those who did not (Group B) were compared. Results: There was no seizure or magnesium toxicity in this cohort. Median (min–max) level of serum magnesium was 4.3 (2.5–8.4) mg/dL. Women in Group A (n = 105) had lower gestational age, body mass index (BMI), and platelets count, higher blood urea nitrogen (BUN), serum creatinine, uric acid, direct bilirubin, aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, prothrombin, and partial thromboplastin times than those in Group B (n = 255) (p <.05). Women with mild PE were less likely to attain therapeutic serum magnesium levels compared with those with severe phenotypes (adjusted OR 23.57, 95% CI 8.20–67.76 versus adjusted OR 14.72, 95% CI 3.56–60.89, respectively; p <.05), which may be explained by their significantly lower serum BUN and uric acid (p <.05). Conclusions: On-admission factors, especially BMI and renal clearance indices, of women with PE may affect timely attainment of therapeutic serum magnesium levels. Validation of its clinical impact requires further study focusing on women with severe PE.