Serum magnesium and calcium ions in patients with severe pre-eclampsia/eclampsia undergoing magnesium sulfate therapy.

BACKGROUND: Magnesium sulfate is used for seizure therapy and prophylaxis in women with eclampsia and preeclampsia worldwide. Magnesium may act by opposing calcium-dependent arterial constriction and may also antagonize the increase in intracellular calcium concentration. The objectives were to study the alterations in serum ionized magnesium and calcium and their relationship in patients with severe pre-eclampsia/eclampsia receiving magnesium sulfate therapy. MATERIAL/
METHODS: Fifty patients in singleton pregnancy with severe pre-eclampsia or eclampsia who were candidates for intravenous magnesium sulfate infusion were studied. Serum ionized magnesium and calcium concentration were determined in blood samples taken before magnesium sulfate infusion, 30 and 240 minutes after the initiation of the infusion, and 4 hours after discontinuation of the therapy. Repeated-measure ANOVA, paired t-test, and Pearson's correlation coefficient were used to analyze the data.
RESULTS: Mean baseline levels of ionized magnesium and ionized calcium were 1.3+/-0.5 mEq/l and 3.8+/-0.5 mg/dl, respectively. The mean concentration of ionized magnesium changed significantly at the stated intervals, while mean ionized calcium values did not. Significant correlation was found between ionized calcium and magnesium four hours after the initiation of magnesium sulfate infusion and after discontinuation of the therapy.
CONCLUSIONS: Magnesium ion does not appear to exert its therapeutic effect in pre-eclampsia/eclampsia by substantially modulating serum ionized calcium. However, the effect of exogenous Mg on intracellular calcium cannot be ruled out.