Serum ionized magnesium during magnesium sulfate administration for preterm labor and preeclampsia

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.

Total and ionized serum magnesium and calcium levels during magnesium sulfate administration for preterm labor

Objective

This study aimed to estimate the association between total and ionized magnesium, and the changes in serum magnesium and calcium levels in patients with preterm labor during magnesium sulfate (MgSO₄) administration.

Methods

The study population included 64 women who were candidates for intravenous MgSO₄ treatment for preterm labor. Serial blood samples were taken and measured total magnesium (T-Mg), ionized magnesium (I-Mg), total calcium (T-Ca), and ionized calcium (I-Ca) levels every one-week interval (1st, 2nd, 3rd).

Results

There was no significant difference in T-Mg and I-Mg levels during MgSO₄ administration (P>0.05). There was no significant difference in T-Ca and I-Ca levels during MgSO₄ administration (P>0.05). Compared before and after administration of MgSO₄, T-Mg and I-Mg levels and T-Ca levels were changed allow statistically significant (P<0.05). But, there was no significant difference in the I-Ca serum levels before and after MgSO₄ administration (P=0.495). The I-Mg levels for patients with adverse effect were higher than other group but did not reach statistical significance (P>0.05). There was significant correlation between levels of I-Mg and T-Mg (I-Mg=0.395×T-Mg+0.144, P<0.01).

Conclusion

There were no significant differences in serum Mg and Ca levels during MgSO₄ administration for preterm labor. Compared to the before and after administration of MgSO₄, only I-Ca levels were not substantially changed. There are significant correlations between I-Mg and T-Mg levels during administration of MgSO₄ and I-Mg level seemed to have more correlation with adverse effect than T-Mg.

High-Dose Magnesium Sulfate Infusion for Severe Asthma in the Emergency Department: Efficacy Study

OBJECTIVE

To assess the efficacy of a high-dose prolonged magnesium sulfate infusion in patients with severe, noninfectious-mediated asthma.

DESIGN

Prospective, randomized, open-label study.

SETTING

Twenty-nine-bed pediatric emergency department located in a children's hospital in Asuncion, Paraguay.

PATIENTS

All patients of 6-16 years old who failed to improve after 2 hours of standard therapy for asthma.

INTERVENTIONS

Subjects were randomized to receive magnesium sulfate, 50 mg/kg over 1 hour (bolus) or high-dose prolonged magnesium sulfate infusion of 50 mg/kg/hr for 4 hours (max, 8.000 mg/4 hr). Patients were monitored for cardiorespiratory complications.

MEASUREMENTS AND MAIN RESULTS

Asthma severity was assessed via asthma scores and peak expiratory flow rates at 0-2-6 hours. The primary outcome was discharge to home at 24 hours. An analysis of the hospital length of stay and costs was a secondary outcome. Thirty-eight patients were enrolled, 19 in each group. The groups were of similar ages, past medical history of asthma, asthma score, and peak expiratory flow rate. There was a significant difference in the patients discharged at 24 hours: 47% in high-dose prolonged magnesium sulfate infusion (9/19) versus 10% (2/21) in the bolus group (p = 0.032) with an absolute risk reduction 37% (95% CI, 10-63) and a number needed to treat of 2.7 (95% CI, 1.6-9.5) to facilitate a discharge at or before 24 hours. The length of stay was shorter in the high-dose prolonged magnesium sulfate infusion group (mean ± SD in hr: high-dose prolonged magnesium sulfate infusion, 34.13 ± 19.54; bolus, 48.05 ± 18.72; p = 0.013; 95% CI, 1.3-26.5). The cost per patient in the high-dose prolonged magnesium sulfate infusion group was one third lower than the bolus group (mean ± SD: high-dose prolonged magnesium sulfate infusion, $603.16 ± 338.47; bolus, $834.37 ± 306.73; p < 0.016). There were no interventions or discontinuations of magnesium sulfate due to adverse events.

CONCLUSIONS

The early utilization of high-dose prolonged magnesium sulfate infusion (50 mg/kg/hr/4 hr), for non-infectious mediated asthma, expedites discharges from the emergency department with significant reduction in healthcare cost.

Clinical pharmacokinetic properties of magnesium sulphate in women with pre-eclampsia and eclampsia

BACKGROUND

The pharmacokinetic basis of magnesium sulphate (MgSO4 ) dosing regimens for eclampsia prophylaxis and treatment is not clearly established.

OBJECTIVES

To review available data on clinical pharmacokinetic properties of MgSO4 when used for women with pre-eclampsia and/or eclampsia.

SEARCH STRATEGY

MEDLINE, EMBASE, CINAHL, POPLINE, Global Health Library and reference lists of eligible studies.

SELECTION CRITERIA

All study types investigating pharmacokinetic properties of MgSO4 in women with pre-eclampsia and/or eclampsia.

DATA COLLECTION AND ANALYSIS

Two authors extracted data on basic pharmacokinetic parameters reflecting the different aspects of absorption, bioavailability, distribution and excretion of MgSO4 according to identified dosing regimens.

MAIN RESULTS

Twenty-eight studies investigating pharmacokinetic properties of 17 MgSO4 regimens met our inclusion criteria. Most women (91.5%) in the studies had pre-eclampsia. Baseline serum magnesium concentrations were consistently <1 mmol/l across studies. Intravenous loading dose between 4 and 6 g was associated with a doubling of this baseline concentration half an hour after injection. Maintenance infusion of 1 g/hour consistently produced concentrations well below 2 mmol/l, whereas maintenance infusion at 2 g/hour and the Pritchard intramuscular regimen had higher but inconsistent probability of producing concentrations between 2 and 3 mmol/l. Volume of distribution of magnesium varied (13.65-49.00 l) but the plasma clearance was fairly similar (4.28-5.00 l/hour) across populations.

CONCLUSION

The profiles of Zuspan and Pritchard regimens indicate that the minimum effective serum magnesium concentration for eclampsia prophylaxis is lower than the generally accepted level. Exposure-response studies to identify effective alternative dosing regimens should target concentrations achievable by these standard regimens.

TWEETABLE ABSTRACT

Minimum effective serum magnesium concentration for eclampsia prophylaxis is lower than the generally accepted therapeutic level.

High-dose magnesium sulfate infusion protocol for status asthmaticus: a safety and pharmacokinetics cohort study

PURPOSE

To assess the safety and pharmacokinetics of high-dose magnesium sulfate (MgSO(4)) infusion in pediatric patients with status asthmaticus.

METHODS

A prospective cohort study within a 20-bed pediatric intensive care unit in an academic community hospital. Patients 2-18 years of age admitted with status asthmaticus between 10/2009 and 8/2010 were included in the study. All patients received standard therapy for asthma, while the treatment group received an intravenous magnesium sulfate bolus of 50-75 mg/kg (0.2-0.3 mmol/kg) followed by 40 mg/kg/h (0.16 mmol/kg/h) for 4 h. Patients were monitored for cardiorespiratory complications. The treatment group underwent four blood draws to assess pharmacokinetic parameters.

RESULTS

Nineteen patients were in the treatment group and 38 patients in the control group after exclusion criteria and consenting were completed. No clinically significant differences were found between groups. There were no interventions or discontinuations of MgSO(4) due to adverse events. In the treatment group, three patients had mild infusion-related reactions. Heart rate and respiratory rate were statistically significantly lower in the magnesium treatment group.

CONCLUSIONS

The continuous infusions of MgSO(4) were safe at the studied doses and maintained serum magnesium (SrMg) and ionized magnesium levels similar to levels required to produce smooth muscle relaxation in other clinical settings. Further studies are needed to investigate the efficacy of high-dose continuous MgSO(4) infusion as an adjunctive treatment for severe asthma treatment and determine the SrMg level required to maintain airway smooth muscle relaxation.

Feasibility of short-term infusion of magnesium sulfate in pediatric patients with status asthmaticus

OBJECTIVE

This report describes the feasibility of high-dose magnesium sulfate infusion in pediatric patients with status asthmaticus.

METHODS

Retrospective chart review over a 3-year period of all patients younger than 18 years of age with status asthmaticus who underwent a high-dose magnesium sulfate infusion for 4 hours. All patients were breathing spontaneously but were refractory to conventional therapy. The magnesium sulfate infusion regimen was 50 mg/kg (for patients weighing >30 kg) or 75 mg/kg (for those weighing ≤30 kg) over a period of 30 to 45 minutes, followed by a continuous infusion of 40 mg/kg/hr for 4 hours. Information regarding vital and clinical respiratory signs, serum magnesium (SrMg), ionized magnesium (iMg), electrocardiograms, and cardiac troponin levels were retrieved. We analyzed the relationship between SrMg and iMg by using linear regression analysis.

RESULTS

Nineteen patients were included. At the end of the infusion, SrMg levels were 4.4 ± 0.8 mg/dL, and iMg levels were 0.95 ± 0.2 mmol/L. SrMg levels only moderately predicted iMg (r(2) = 0.541). There were no reports of hypotension, respiratory failure, neurological problems, or nausea. Discomfort at the site of infusion was reported in three cases. Troponin levels (n = 12) and electrocardiograms (n = 12), when available, were noted at the end of the infusion and were normal in all patients p=0.01.

CONCLUSIONS

In this case series, short-term high-dose administration of magnesium sulfate in the context of status asthmaticus was feasible, and we did not observe clinical complications with its use. Total SrMg was inadequate to reflect the active form of magnesium, iMg. The dose used achieved theoretical therapeutic levels of iMg.

Umbilical artery pH may be a possible confounder for neonatal adverse outcomes in preterm infants exposed to antenatal magnesium

OBJECTIVES

To determine the normal range of ionized magnesium (IMg) levels in cord blood during preterm gestation and to investigate whether antenatal Mg administration affects neonatal intraventricular hemorrhage (IVH) or patent ductus arteriosus (PDA).

METHODS

In this retrospective case-control study, we reviewed 118 pregnant women with antenatal Mg administration and their infants after they gave birth at one tertiary care center between January 2006 and December 2010. Thirty-seven cases with IVH and/or PDA were compared to 81 controls by multiple logistic regression analysis. The normal range of IMg levels was determined by another 79 subjects without any tocolytic agents and possible confounders. Perinatal and neonatal characteristics were then compared between three groups divided by the IMg levels in cord serum.

RESULTS

The normal range of IMg levels in cord blood was determined to be 0.47 ± 0.07 mmol/L, regardless of gestational weeks. IMg level in cord serum could not be a risk factor for IVH or PDA. Elevation of IMg level in cord blood resulted in an increased incidence of IVH and a decreased incidence of PDA, but not significantly. IMg level in cord blood was inversely correlated with umbilical artery pH (p = 0.067).

CONCLUSIONS

There was no significant relationship between the IMg levels in cord serum and neonatal IVH and PDA. Umbilical artery pH may be a possible confounder.

Ionized and total magnesium concentration in patients with severe preeclampsia-eclampsia undergoing magnesium sulfate therapy

AIM

As ionized magnesium is the active form of magnesium and exerts a therapeutic effect, the present study was performed to determine the levels and correlations between ionized and total magnesium under baseline and therapeutic conditions in patients with severe preeclampsia and eclampsia receiving magnesium sulfate.

METHODS

Fifty singleton patients with severe preeclampsia received a loading dose of 4 g of magnesium sulfate, followed by 2 g per hour as maintenance dose until 24 h after delivery, or 24 h after the last seizure in case of postpartum convulsions. Serial blood samples were taken before magnesium sulfate infusion, 30 min and 240 min after the initiation of the infusion and 4 h after the discontinuation of the drug. Data were analyzed by repeated measure ANOVA and paired t-test.

RESULTS

Baseline levels of total and ionized magnesium were 2.4+/-0.6 mEq/L and 1.3+/-0.5 mEq/L (mean+/-SD), respectively. Putative level of 4 mEq/L of total magnesium was not obtained in up to 42% of patients during the treatment. There was not any significant correlation between the two forms of magnesium under baseline and therapeutic conditions.

CONCLUSION

Despite the effectiveness of the standard regimen of magnesium sulfate in the treatment and prevention of eclamptic seizures, it can not provide the proposed therapeutic level of magnesium in all patients. With respect to the lack of correlation between ionized and total magnesium, further studies are necessary to investigate the superiority of measurement of ionized, rather than total magnesium, for titration of therapeutic magnesium sulfate infusion.