Serum magnesium levels during magnesium sulfate infusion at 1 gram/hour versus 2 grams/hour as a maintenance dose to prevent eclampsia in women with severe preeclampsia: A randomized clinical trial

BACKGROUND

Magnesium sulfate is the ideal drug for the prevention and treatment of eclampsia. Nevertheless, the best regimen for protection against eclampsia with minimal side effects remains to be established. This study aimed to compare serum magnesium levels during intravenous infusion of magnesium sulfate at 1 gram/hour versus 2 grams/hour as a maintenance dose to prevent eclampsia in pregnant and postpartum women with severe preeclampsia.

METHODS

A randomized, triple-blind clinical trial was conducted, comparing serum magnesium levels during the intravenous infusion of magnesium sulfate at 1 gram/hour versus 2 grams/hour as a maintenance dose for the prevention of eclampsia in 62 pregnant and postpartum women with severe preeclampsia, 31 in each group. An intravenous loading dose of 6 grams of magnesium sulfate was administered over 30 minutes in both groups. The patients were then randomized to receive a maintenance dose of either 1 or 2 grams/hour for 24 hours. Primary outcomes consisted of serum magnesium levels at the following time points: baseline, 30 minutes, every 2 hours until the end of the first 6 hours, and every 6 hours thereafter until the termination of magnesium sulfate infusion. Side effects, maternal complications, and neonatal outcomes were the secondary outcomes.

RESULTS

Serum magnesium levels were higher in the 2-gram/hour group, with a statistically significant difference from 2 hours after the beginning of the magnesium sulfate infusion (P <.05). Oliguria was the most common complication recorded in both groups, with no significant difference between the 2 regimens (RR 0.88; 95% CI: 0.49-1.56; P = .65). No cases of eclampsia occurred. Side effects were more common in the 2-gram/hour group (RR 1.89; 95% CI: 1.04-3.41; P = .02); however, all were mild. There were no differences between the 2 groups regarding neonatal outcomes, except for admission to neonatal intensive care, which was more frequent in the 1-gram/hour group (25% vs 6.3%; P = .04).

CONCLUSION

Magnesium sulfate therapy at the maintenance dose of 1 gram/hour was just as effective as the 2-gram maintenance dose, with fewer side effects.

Assessing the neuroprotective benefits for babies of antenatal magnesium sulphate: An individual participant data meta-analysis

BACKGROUND

Babies born preterm are at an increased risk of dying in the first weeks of life, and those who survive have a higher rate of cerebral palsy (CP) compared with babies born at term. The aim of this individual participant data (IPD) meta-analysis (MA) was to assess the effects of antenatal magnesium sulphate, compared with no magnesium treatment, given to women at risk of preterm birth on important maternal and fetal outcomes, including survival free of CP, and whether effects differed by participant or treatment characteristics such as the reason the woman was at risk of preterm birth, why treatment was given, the gestational age at which magnesium sulphate treatment was received, or the dose and timing of the administration of magnesium sulphate.

METHODS AND FINDINGS

Trials in which women considered at risk of preterm birth (<37 weeks' gestation) were randomised to magnesium sulphate or control treatment and where neurologic outcomes for the baby were reported were eligible for inclusion. The primary outcomes were infant death or CP and severe maternal outcome potentially related to treatment. Studies were identified based on the Cochrane Pregnancy and Childbirth search strategy using the terms [antenatal or prenatal] and [magnesium] and [preterm or premature or neuroprotection or 'cerebral palsy']. The date of the last search was 28 February 2017. IPD were sought from investigators with eligible trials. Risk of bias was assessed using criteria from the Cochrane Collaboration. For each prespecified outcome, IPD were analysed using a 1-stage approach. All 5 trials identified were included, with 5,493 women and 6,131 babies. Overall, there was no clear effect of magnesium sulphate treatment compared with no treatment on the primary infant composite outcome of death or CP (relative risk [RR] 0.94, 95% confidence interval (CI) 0.85 to 1.05, 6,131 babies, 5 trials, p = 0.07 for heterogeneity of treatment effect across trials). In the prespecified sensitivity analysis restricted to data from the 4 trials in which the intent of treatment was fetal neuroprotection, there was a significant reduction in the risk of death or CP with magnesium sulphate treatment compared with no treatment (RR 0.86, 95% CI 0.75 to 0.99, 4,448 babies, 4 trials), with no significant heterogeneity (p = 0.28). The number needed to treat (NNT) to benefit was 41 women/babies to prevent 1 baby from either dying or having CP. For the primary outcome of severe maternal outcome potentially related to magnesium sulphate treatment, no events were recorded from the 2 trials providing data. When the individual components of the composite infant outcome were assessed, no effect was seen for death overall (RR 1.03, 95% CI 0.91 to 1.17, 6,131 babies, 5 trials) or in the analysis of death using only data from trials with the intent of fetal neuroprotection (RR 0.95, 95% CI 0.80 to 1.13, 4,448 babies, 4 trials). For cerebral palsy in survivors, magnesium sulphate treatment had a strong protective effect in both the overall analysis (RR 0.68, 95% CI 0.54 to 0.87, 4,601 babies, 5 trials, NNT to benefit 46) and the neuroprotective intent analysis (RR 0.68, 95% CI 0.53 to 0.87, 3,988 babies, 4 trials, NNT to benefit 42). No statistically significant differences were seen for any of the other secondary outcomes. The treatment effect varied little by the reason the woman was at risk of preterm birth, the gestational age at which magnesium sulphate treatment was given, the total dose received, or whether maintenance therapy was used. A limitation of the study was that not all trials could provide the data required for the planned analyses so that combined with low event rates for some important clinical events, the power to find a difference was limited.

CONCLUSIONS

Antenatal magnesium sulphate given prior to preterm birth for fetal neuroprotection prevents CP and reduces the combined risk of fetal/infant death or CP. Benefit is seen regardless of the reason for preterm birth, with similar effects across a range of preterm gestational ages and different treatment regimens. Widespread adoption worldwide of this relatively inexpensive, easy-to-administer treatment would lead to important global health benefits for infants born preterm.

Pharmacokinetics and placental transfer of magnesium sulfate in pregnant women

BACKGROUND

Magnesium sulfate is one of the most commonly prescribed intravenous medications in obstetrics. Despite its widespread use, there are limited data about magnesium pharmacokinetics, and magnesium is prescribed empirically without dose adjustment for different indications.

OBJECTIVE

The aim of this study was to characterize the pharmacokinetics and placental transfer of magnesium sulfate in pregnant women and to determine key covariates that impact the pharmacokinetics.

STUDY DESIGN

This is a prospective pharmacokinetic cohort study of pregnant women who were prescribed magnesium sulfate for preeclampsia, preterm labor, or extreme prematurity. Women received a 4-g loading dose and 2 g/h maintenance dose as clinically indicated. Maternal blood samples were obtained before and at multiple time points during and after magnesium administration. Cord blood also was sampled at delivery. A population pharmacokinetic approach that used a nonlinear mixed-effects modeling was used to characterize magnesium disposition.

RESULTS

Pharmacokinetic profiles of 111 pregnant women were analyzed. Magnesium clearance was 3.98 L/h in preeclamptic women and 5.88 L/h non-preeclamptic women. Steady-state concentration of magnesium was 7.2 mg/dL in preeclamptic women compared with 5.1 mg/dL in non-preeclamptic women. Maternal weight significantly impacted time to steady state. The ratio of the mean umbilical vein magnesium level to the mean maternal serum magnesium level at the time of delivery was 0.94 ± 0.15.

CONCLUSIONS

The study accurately characterizes the pharmacokinetics of magnesium administered to pregnant women. Preeclamptic status and maternal weight significantly impact serum magnesium levels. This pharmacokinetic model could be applied to larger cohorts to help tailor magnesium treatment and account for these covariates.

Hydration with 15 mEq Magnesium Is Effective at Reducingthe Risk for Cisplatin-induced Nephrotoxicity in Patients Receiving Cisplatin (≥50 mg/m2) Combination Chemotherapy

AIM

We aimed to assess whether the efficacy of pre-hydration with 15 mEq magnesium prevents cisplatin-induced nephrotoxicity in cisplatin regimens (dosage: 50 mg/m(2)or more) for gynecological cancer.

PATIENTS AND METHODS

This historical, prospective cohort study compared nephrotoxicity in patients who received pre-hydration with or without magnesium sulfate (Mg-hydration group, n=37; non-Mg-hydration group, n=37). We used serum creatinine (Scr), creatinine clearance (Ccr) and Risk, Injury, Failure, Loss of kidney function and End-stage kidney disease (RIFLE) criteria.

RESULTS

A change of Scr and Ccr in the Mg-hydration group was higher than in the non-Mg-hydration group. Based on the RIFLE criteria, the number of moderate renal dysfunction patients classified as "Risk" in the Mg-hydration group was significantly lower than in the non-Mg-hydration group (Mg-hydration group=21.6%; non-Mg-hydration group=51.4%; p<0.01). Serum magnesium levels in the Mg-hydration group significantly declined during chemotherapy (p<0.01).

CONCLUSION

We found that a 15 mEq magnesium as pre-hydration provided nephroprotective effects in patients receiving this cisplatin regimen. Future research should involve finding appropriate magnesium doses.

Association of cord blood magnesium concentration and neonatal resuscitation

OBJECTIVE

To assess the relationship between umbilical cord blood magnesium concentration and level of delivery room resuscitation received by neonates.

STUDY DESIGN

This was a secondary analysis of a controlled fetal neuroprotection trial that enrolled women at imminent risk for delivery between 24 and 31 weeks' gestation and randomly allocated them to receive either intravenous magnesium sulfate or placebo. The cohort included 1507 infants with data available on total cord blood Mg concentration and delivery room resuscitation. Multivariate logistic regression was used to estimate the association between cord blood Mg concentration and highest level of delivery room resuscitation, using the following hierarchy: none, oxygen only, bag-mask ventilation with oxygen, intubation, and chest compressions.

RESULTS

There was no relationship between cord blood Mg and delivery room resuscitation (OR, 0.92 for each 1.0-mEq/L increase in Mg; 95% CI, 0.83-1.03). Maternal general anesthesia was associated with increased neonatal resuscitation (OR, 2.51; 95% CI, 1.72-3.68). Each 1-week increase in gestational age at birth was associated with decreased neonatal resuscitation (OR, 0.63; 95% CI, 0.60-0.66).

CONCLUSION

Cord blood Mg concentration does not correlate with the level of delivery room resuscitation of infants exposed to magnesium sulfate for fetal neuroprotection.

Use of magnesium sulfate in pre-eclampsia and eclampsia in teaching hospitals in Addis Ababa: a practice audit

BACKGROUND

Magnesium sulphate is shown to be the drug of choice in the management of severe pre-eclampsia-eclampsia for over two decades. However, the drug was introduced in practice in teaching hospitals in Addis Ababa recently. Hence, it is important to audit its use at this stage.

OBJECTIVES

To audit the experience of magnesium sulfate use for management of severe pre-eclampsia and eclampsia on its introduction in teaching hospitals in Addis Ababa.

METHODOLOGY

A retrospective medical record review was conducted to audit use of magnesium sulfate, MgSO4, in two teaching hospitals in Addis Ababa between February and August 2006.

RESULTS

One hundred three women received magnesium sulfate during the study period (February to August, 2006). It was possible to retrieve the charts of 95 women (92.2% chart retrieval rate). Seventy-four percent (54/73) of the eligible cases from Tikur Anbesa Hospital and 63.6% (49/77) from Gandhi Memorial Hospital received the drug. Patient selection for administration of magnesium sulfate was appropriate in 93.7% (89/95) of women with hypertension in pregnancy. Correct loading dose of MgSO4 was given for 90.4% (85/95) of the patients. No woman with severe pre-eclampsia convulsed after initiation of magnesium sulfate, while four of the eclamptic mothers had recurrence of seizures. The overall clinical monitoring of patients who were on treatment was inadequate with respect to the protocol of the hospitals. Only one (1.1%) woman was reported to have developed signs of a major side effect of magnesium sulfate and two mothers died. Both of these deaths were not attributed to magnesium sulfate toxicity.

CONCLUSION AND RECOMMENDATIONS

This study showed that a good proportion (more than two-thirds) of the eligible cases has received magnesium sulfate. It is recommended that the respective hospitals should give due attention to the suboptimal patient monitoring.

An audit of the use of magnesium sulphate in severe pre-eclampsia and eclampsia

Over the last decade there has been an increase in the use of MgSO4 for the prevention of seizures in women with severe pre-eclampsia or eclampsia. At the Rotunda Hospital it is regularly used for this purpose. The aim of this study was to audit the use of MgSO4 at the hospital, to determine whether the drug was being used according to the hospital's protocol and to observe its effectiveness in the prevention of eclampsia in our population. A retrospective chart review over the two years from 1/1/2000 to 31/12/2001 was undertaken. Outcome measures assessed were; Patient selection, Administration of the drug - whether recommended protocols were adhered, Effectiveness of therapy for seizure prophylaxis, Maternal and neonatal outcomes. There were 12,910 deliveries at the Rotunda hospital over this period of time. Fifty of these women were treated with MgSO4 (0.4%). Patient selection was appropriate in all cases. The correct loading dose of MgSO4 was administered in all cases, however MgSO4 levels were recorded in only 30 (60%) of women. There were no seizures in the treated group. Two women presented with seizures (one was antenatal the other post-natal period), both were treated with MgSO4. There were no maternal or neonatal mortality. Seventy two percent (36) of these women were delivered by lower segment caesarean section. The mean gestation at delivery was 36 weeks (range 28-41 weeks). Thirty eight percent (13) of babies required admission to the neonatal intensive care unit. The mean birth weight at delivery was 2.54 kg (range 1.11-3.68 kg). MgSO4 use in the Rotunda hospital appears to be safe and effective for the prevention of seizures in women with severe pre-eclampsia or eclampsia. Serum MgSO4 levels were only recorded in 60% of patients and the hospital's protocol was not adhered to regarding monitoring of patients on treatment. This needs to be addressed.

Thiopental and halothane dose-sparing effects of magnesium sulphate in dogs

OBJECTIVE

To evaluate the effect of pre- and intraoperatively administered magnesium sulphate (MgSO(4)) on the induction dose of thiopental and of halothane for maintenance of anaesthesia in dogs undergoing ovariohysterectomy (OHE).

STUDY DESIGN

Prospective, double-blind, randomized, placebo-controlled study.

ANIMALS

Forty-six healthy, ASA physical status 1 dogs, scheduled for elective OHE.

METHODS

The dogs were randomly assigned to receive a bolus of 50 mg kg(-1) MgSO(4) intravenously (IV), just before induction of anaesthesia, followed by a constant rate infusion (CRI) of 12 mg kg(-1) hour(-1) MgSO(4) intraoperatively (group Mg, n = 27) or a placebo bolus and CRI of 0.9% sodium chloride (NaCl) (group C, n = 19), approximately 30 minutes after premedication with acepromazine (0.05 mg kg(-1), intramuscularly, IM) and carprofen (4 mg kg(-1), subcutaneously, SC). Anaesthesia was induced with thiopental administered to effect and maintained with halothane in oxygen. End-tidal halothane (ET(hal)) was adjusted to achieve adequate depth of anaesthesia. Blood samples were obtained pre- and postoperatively for measurement of total serum magnesium concentration.

RESULTS

The mean dose of thiopental was statistically lower (p < 0.0005) and the mean standardized ET(hal) concentration and end-tidal carbon dioxide partial pressure (Pe'CO(2)) areas under the curve were statistically smaller (p < 0.0005 and 0.014 respectively) in group Mg. Postoperatively the mean total serum magnesium concentration was statistically higher than the preoperative value (p < 0.0005) in group Mg, but not in group C. Nausea, associated with the MgSO(4) bolus injection, was observed in six dogs in group Mg, two of which vomited prior to induction of anaesthesia.

CONCLUSIONS AND CLINICAL RELEVANCE

Magnesium sulphate administration reduced the induction dose of thiopental and ET(hal) concentration for maintenance of anaesthesia in dogs undergoing OHE. Observed side effects were nausea and vomiting.

Efficacy and vasodilatory benefit of magnesium prophylaxis for protection against spinal cord ischemia

Prevention of paraplegia remains an imperative issue in thoracoabdominal aortic surgery. The aim of this study was to assess the efficacy of a prophylactic magnesium infusion in a rat spinal cord ischemia model and to demonstrate spinal blood flow increase caused by the infusion. The study was conducted in two parts. Firstly, the neuroprotective effect of magnesium was assessed using a rat model with two different ischemic times: 10 min and 14 min. Spinal cord ischemia was induced by occlusion of the descending aorta. Rats in the treatment group were given a 100 mg/kg magnesium sulfate infusion before ischemia. Secondly, relative changes in spinal cord blood flow before and during ischemia were recorded using the laser Doppler flowmetry technique. Changes in blood flow were compared between the magnesium and control groups. Rats pretreated with magnesium showed good overall recovery after both 10 min (incidence of paraplegia 62.5% control vs. 37.5% Mg, n = 8 each) and 14 min (85.7% control vs. 57.1% Mg, n = 7 each) of ischemia, although the differences compared with controls were statistically insignificant. However, the magnesium group showed significantly better neurological performance during the early postischemic period. Comparison of changes in spinal circulation revealed less reduction in blood flow during ischemia in the magnesium-treated group. In conclusion, magnesium may have potential prophylactic benefits during ischemia by exerting a neuroprotective effect through vasodilation of the spinal cord vasculature. To our knowledge, this vasodilatory effect on the spinal cord has not previously been investigated. Optimization of the treatment regimen, however, is required.

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.

Effects of ketamine and magnesium on the minimum alveolar concentration of isoflurane in goats

OBJECTIVE

To evaluate the effects of ketamine, magnesium sulfate, and their combination on the minimum alveolar concentration (MAC) of isoflurane (ISO-MAC) in goats.

ANIMALS

8 adult goats.

PROCEDURES

Anesthesia was induced with isoflurane delivered via face mask. Goats were intubated and ventilated to maintain normocapnia. After an appropriate equilibration period, baseline MAC (MAC(B)) was determined and the following 4 treatments were administered IV: saline (0.9% NaCl) solution (loading dose [LD], 30 mL/20 min; constant rate infusion [CRI], 60 mL/h), magnesium sulfate (LD, 50 mg/kg; CRI, 10 mg/kg/h), ketamine (LD, 1 mg/kg; CRI, 25 microg/kg/min), and magnesium sulfate (LD, 50 mg/kg; CRI, 10 mg/kg/h) combined with ketamine (LD, 1 mg/kg; CRI, 25 microg/kg/min); then MAC was redetermined.

RESULTS

Ketamine significantly decreased ISOMAC by 28.7 +/- 3.7%, and ketamine combined with magnesium sulfate significantly decreased ISOMAC by 21.1 +/- 4.1%. Saline solution or magnesium sulfate alone did not significantly change ISOMAC.

CONCLUSIONS AND CLINICAL RELEVANCE

Ketamine and ketamine combined with magnesium sulfate, at doses used in the study, decreased the end-tidal isoflurane concentration needed to maintain anesthesia, verifying the clinical impression that ketamine decreases the end-tidal isoflurane concentration needed to maintain surgical anesthesia. Magnesium, at doses used in the study, did not decrease ISOMAC or augment ketamine's effects on ISOMAC.

Magnesium sulfate exposure increases fetal blood flow redistribution to the brain during acute non-acidemic hypoxemia in goats

BACKGROUND

It is still controversial that intrapartum exposure to magnesium may or may not reduce brain damage in premature infants in human and animal models.

AIMS

We investigated the effect of hypoxemia alone under magnesium exposure on fetal cardiovascular changes in chronically catheterized goat fetuses.

STUDY DESIGN

We performed a 3-day experimental protocol with control (10% glucose) on day 1, recovery on day 2, and magnesium on day 3. Magnesium sulfate was directly infused to fetuses in a bolus dose of 270 mg/kg followed by 80 mg/kg/h. Hypoxemia was induced by maternal inhalation of nitrogen gas on day 1 and on day 3. Cerebral blood flow was measured by colored microsphere techniques. Repeated measure ANOVA and Bonferroni's/Dunn's test were used for comparison.

SUBJECTS

Six Japanese Saanen goats at 0.85 gestation.

OUTCOME MEASURES

Fetal heart rate, blood pressure, and cerebral blood flow.

RESULTS

Ionized magnesium concentrations were significantly increased. Fetal PO2 decreased significantly from 30 mmHg to 14 mmHg without acidemia. Magnesium exposure significantly attenuated hypoxemia-induced bradycardia but did not affect blood pressure. Hypoxemia significantly increased fetal brain blood flow from the pre-hypoxic levels on day 1. Magnesium exposure further increased hypoxemia-induced brain blood flow on day 3, but statistical significance was limited to the cerebral cortex.

CONCLUSION

In near-term, initially healthy goat fetuses, brain blood flow during acute hypoxemia was significantly increased with magnesium sulfate exposure.

[Effect of magnesium sulfate on fetal rats of fetal growth retardation and its relation with expression of caspase-3 on the placenta of maternal rat]

OBJECTIVE

To investigate the effect of magnesium sulfate on the fetal rats of fetal growth retardation (FGR) and its relation with expression of caspase-3 on the placenta of maternal rat.

METHODS

Model of FGR was constructed according to the method of passive smoking. The pregnant rats were divided into control group (n = 10), therapy group (n = 18) and FGR group (n = 10). The therapy group rats were given different doses of magnesium sulfate by subcutaneous injection: low dose group (300 mg/kg, n = 10), high dose group (600 mg/kg, n = 8). Serum concentration of magnesium sulfate was monitored. The expression of caspase-3 was measured by immunohistochemistry method and RT-PCR.

RESULTS

Both of the concentration of magnesium sulfate in high and low dose groups (0.72 +/- 0.13), (0.61 +/- 0.03) mmol/L were higher than the FGR group (0.55 +/- 0.03) mmol/L (P < 0.01); the weight of placenta and fetal rat in high dose group [(0.80 +/- 0.16) and (3.58 +/- 0.10) g] were more than those of FGR group [(0.63 +/- 0.05) and (2.95 +/- 0.46) g] (P < 0.05, P < 0.01); the expression of mRNA and protein of caspase-3 in high dose group [(0.361 +/- 0.030), (183.0 +/- 3.3)] was lower than the FGR group [(0.626 +/- 0.036), (199.5 +/- 4.7)] (P < 0.05); the expression of mRNA in low dose group (0.525 +/- 0.029) was higher than the high dose group (P < 0.05); serum concentration of magnesium sulfate of maternal rat was correlated with the weight of fetal rat (r = 0.899, P = 0.038) and the expression of mRNA and protein of caspase-3 in placenta (r = -0.747, P = 0.033; r = -0.915, P = 0.001).

CONCLUSION

It is suggested that magnesium sulfate increases the weight of fetal rat probably by depressing the expression of caspase-3 of placenta, which improves the placental function.

Magnesium sulfate neither potentiates nor inhibits tissue plasminogen activator-induced thrombolysis

BACKGROUND

Increasing circulating magnesium concentrations to 2-fold over normal baseline may afford a neuroprotective effect in patients with acute cerebral ischemia.

OBJECTIVES

As patients receiving magnesium sulfate (MgSO(4)) in human clinical trials may also be candidates for subsequent thrombolytic therapy with tissue plasminogen activator (t-PA), preclinical assessment of possible inhibition or potentiation of fibrinolytic activity by MgSO(4) has important clinical relevance.

METHODS

We utilized an in vitro system, in which D-dimer release served as a reflection of t-PA-induced clot lysis, to measure the effect of magnesium at the target concentration being tested in human stroke clinical trials, and at 2- and 3-fold higher levels. Clots from normal volunteers were exposed to t-PA at concentrations that correspond to therapeutic or endogenous plasma t-PA levels.

RESULTS

MgSO(4) had no effect on t-PA-induced clot lysis at up to 3-fold target magnesium concentration (6x normal serum concentration).

CONCLUSIONS

MgSO(4) concentrations well above the targeted level in therapeutic stroke trials does not affect t-PA-induced fibrinolytic activity, and therefore is a suitable agent for trials of combined neuroprotective and thrombolytic therapy in patients with acute ischemic stroke.

Magnesium as a neuroprotectant in cardiac surgery: A randomized clinical trial

OBJECTIVE

We sought to evaluate magnesium as a neuroprotectant in patients undergoing cardiac surgery with cardiopulmonary bypass.

METHODS

From February 2002 to September 2003, 350 patients undergoing elective coronary artery bypass grafting, valve surgery, or both were enrolled in a randomized, blinded, placebo-controlled trial to receive either magnesium sulfate to increase plasma levels 1(1/2) to 2 times normal during cardiopulmonary bypass (n = 174) or no intervention (n = 176). Neurologic function, neuropsychologic function, and depression were assessed preoperatively, at 24 and 96 hours after extubation (neurologic) and at 3 months (neuropsychologic, depression). Neurologic scores were analyzed using ordinal longitudinal methods, and neuropsychologic and depression inventory data were summarized by principal component analysis, followed by linear regression analysis using component scores as response variables.

RESULTS

Seven (2%) patients had a postoperative stroke, 2 (1%) in the magnesium and 5 (3%) in the placebo group (P = .4). Neurologic score was worse postoperatively in both groups (P < .0001); however, magnesium group patients performed better than placebo group patients (P = .0001), who had prolonged declines in short-term memory and reemergence of primitive reflexes. Three-month neuropsychologic performance and depression inventory score were generally better than preoperatively, with few differences between groups (P > .6); however, older age (P = .0006), previous stroke (P = .003), and lower education level (P = .0007) were associated with worse performance.

CONCLUSIONS

Magnesium administration is safe and improves short-term postoperative neurologic function after cardiac surgery, particularly in preserving short-term memory and cortical control over brainstem functions. However, by 3 months, other factors and not administration of magnesium influence neuropsychologic and depression inventory performance.

Brain lesions in newborns exposed to high-dose magnesium sulfate during preterm labor

High-dosage, tocolytic magnesium sulfate (MgSO4) administered to pregnant women during preterm labor can be toxic, and sometimes lethal, for their newborns (Cochrane Database of Systematic Reviews (relative mortality risk 2.82, 95% confidence interval 1.2-6.6)). Based on the results of the Magnesium and Neurologic Endpoints Trial and the work of many others, a unifying triangular concept is proposed to account for the increased prevalence of brain lesions, with their likely resultant mortality, in neonates and infants exposed to high-dose MgSO4 in the context of preterm labor. We review the evidence that: (1) elevated circulating levels of serum ionized magnesium occurring in mothers, and therefore in their babies, at the time of delivery are associated with subsequent neonatal intraventricular hemorrhage (IVH); (2) neonatal IVH is strongly associated with lenticulostriate vasculopathy (LSV), an unusual mineralizing lesion involving the thalami and basal ganglia of the neonate; and, (3) exposure to 50 g or more of tocolytic MgSO4 during preterm labor is associated with the development of LSV.

Effects of administration of oral magnesium on plasma glucose and pathological changes in the aorta and pancreas of diabetic rats

1. Magnesium deficiency has recently been proposed as a novel factor implicated in the pathogenesis of the complications of diabetes. The purpose of the present study was to determine the relationship between oral Mg supplementation and changes in plasma glucose, calcium, haemoglobin, Ca/Mg ratio, blood pressure and the histology of the pancreas and vascular system in streptozotocin-induced diabetic rats. 2. Ten days after the induction of diabetes in male Wistar rats, half the diabetic animals were divided into six groups, receiving 0, 1, 3, 10, 30 or 50 g/L MgSO4 added into the drinking water for 8 weeks. Plasma glucose and Mg were measured at days 1, 2, 3, 5, 7, 14 and 21 to find the optimum dose of Mg and the time-course of its effect. In addition, histological observations were undertaken. Eight weeks later, all animals were decapitated, the pancreas and thoracic aorta were removed carefully and immersed immediately in 10% formaldehyde for histological study. 3. To evaluate the effects of Mg on plasma glucose, calcium, haemoglobin, Mg and blood pressure, another group of animals was divided into four experimental groups, as follows: (i) non-diabetic controls received tap water for 8 weeks; (ii) acute diabetics received tap water for 10 days; (iii) chronic diabetic controls received tap water for 8 weeks; and (iv) Mg-treated chronic diabetic rats received 10 g/L MgSO4 added into the drinking water 10 days after the induction of diabetes for 8 weeks. 4. Magnesium dose dependently affects plasma glucose levels. The peak effect was reached during the first 24 h following oral administration. Administration of 10 g/L MgSO4 results in the return of normal structure in the diabetic pancreas and aorta. Moreover, this concentration of MgSO4 causes glucose, haemoglobin, calcium, the Ca/Mg ratio and blood pressure to reach normal levels. Although the Mg level increases slightly following the administration of 10 g/L MgSO4 to diabetic rats, it never reaches control levels. 5. On the basis of the results of the present study, it may be concluded that chronic Mg administration may have beneficial effects on diabetes.

Magnesium sulphate only slightly reduces the shivering threshold in humans

BACKGROUND

Hypothermia may be an effective treatment for stroke or acute myocardial infarction; however, it provokes vigorous shivering, which causes potentially dangerous haemodynamic responses and prevents further hypothermia. Magnesium is an attractive anti-shivering agent because it is used for treatment of postoperative shivering and provides protection against ischaemic injury in animal models. We tested the hypothesis that magnesium reduces the threshold (triggering core temperature) and gain of shivering without substantial sedation or muscle weakness.

METHODS

We studied nine healthy male volunteers (18-40 yr) on two randomly assigned treatment days: (1) control and (2) magnesium (80 mg kg(-1) followed by infusion at 2 g h(-1)). Lactated Ringer's solution (4 degrees C) was infused via a central venous catheter over a period of approximately 2 h to decrease tympanic membrane temperature by approximately 1.5 degrees C h(-1). A significant and persistent increase in oxygen consumption identified the threshold. The gain of shivering was determined by the slope of oxygen consumption vs core temperature regression. Sedation was evaluated using a verbal rating score (VRS) from 0 to 10 and bispectral index (BIS) of the EEG. Peripheral muscle strength was evaluated using dynamometry and spirometry. Data were analysed using repeated measures anova; P<0.05 was statistically significant.

RESULTS

Magnesium reduced the shivering threshold (36.3 [SD 0.4] degrees C vs 36.6 [0.3] degrees C, P = 0.040). It did not affect the gain of shivering (control, 437 [289] ml min(-1) degrees C(-1); magnesium, 573 [370] ml min(-1) degrees C(-1); P=0.344). The magnesium bolus did not produce significant sedation or appreciably reduce muscle strength.

CONCLUSIONS

Magnesium significantly reduced the shivering threshold. However, in view of the modest absolute reduction, this finding is considered to be clinically unimportant for induction of therapeutic hypothermia.

Use of magnesium sulphate in severe persistent pulmonary hypertension of the newborn

Persistent pulmonary hypertension in the newborn (PPHN) is a neonatal emergency due to the failure to achieve normal cardiopulmonary adaptation following delivery. A clinical trial to assess the efficacy of magnesium sulphate (MgSO4) in the treatment of PPHN was conducted in the tertiary level neonatal intensive care unit of RIPAS Hospital, Brunei Darussalam over a period of 2 years. Twelve newborn babies admitted consecutively to the neonatal intensive care unit with severe hypoxemia due to persistent pulmonary hypertension were included in this trial. A loading dose of 200 mg/kg MgSO4 was given over a period of 20 min, followed by a continuous infusion at the rate of 20-150 mg/kg/h to obtain a serum magnesium level between 3.5 and 5.5 mmol/l. No other vasodilators were used and babies were not hyperventilated. Dopamine was commenced at 5-10 microg/kg/min before the loading dose of MgSO4 was given. Mean blood pressure was maintained with short periods of dopamine alone or in combination with dobutamine. Oxygen index (OI) and alveolar-arterial oxygen gradient (A-aDO2) showed significant improvement within 24 h of treatment. In this study, MgSO4 was found to be a safe and effective pulmonary vasodilator. MgSO4 could be used as a first-line vasodilator in developing countries because of its low cost and high efficacy. Parenteral MgSO4 is easy to administer and monitor during treatment. When MgSO4 is used, systemic hypotension can be adequately controlled with ionotropes.

Trigeminal schwannoma mimicking magnesium intoxication in a pregnancy complicated by severe preeclampsia

We present a case report describing a pregnancy complicated by severe preeclampsia and a trigeminal schwannoma which caused loss of consciousness, diplopia and blurred vision, which were initially thought to be signs of magnesium intoxication.

Safety of magnesium-lidocaine combination for severe head injury: the Turin lidomag pilot study

BACKGROUND

Neuroprotection in the setting of severe head injury (SHI) remains an unsettled problem. We tested a combination of high-dose magnesium and low-dose lidocaine, infused over 3 days, in a pilot study to assess safety. This combination appears indicated to protect both gray and white matter from secondary injury following SHI.

METHODS

We studied 32 consecutive patients admitted to the emergency department of our hospital, a large tertiary referral center.

RESULTS

No toxicity was observed. Mortality was lower than published statistics.

CONCLUSIONS

These results open the stage to a controlled randomized study.

Intravenous magnesium sulfate prophylaxis for atrial fibrillation after coronary artery bypass surgery

OBJECTIVE

Atrial fibrillation is a rhythm disorder commonly seen early after coronary artery bypass grafting, and it increases morbidity.

METHODS

To investigate the effectiveness of magnesium sulfate in the prophylaxis of atrial fibrillation, we conducted a prospective, randomized, placebo-controlled clinical study on 200 consecutive patients in whom we performed elective and initial coronary artery bypass grafting operations. In each group 50% of patients underwent beating-heart operations. In the treatment group 100 patients (76 men and 24 women; mean age, 57.63 +/- 9.68 years) received 24.34 mEq (3 g) of magnesium sulfate in 100 mL of saline solution that was administered over 2 hours (50 mL/h) preoperatively, perioperatively, and at postoperative days 0, 1, 2, and 3. In the control group 100 patients (74 men and 26 women; mean age, 59.96 +/- 9.29 years) received only 100 mL of saline solution according to the same administration schedule as the treatment group.

RESULTS

Atrial fibrillation developed in 15 patients from the treatment group and in 16 patients from the control group. The arrhythmia developed after 37.87 +/- 12.76 and 45.26 +/- 15.27 hours in the treatment and control groups, respectively. Although a significant relationship was found between low magnesium sulfate levels and increased incidence of atrial fibrillation (P <.05), when the incidence of postoperative atrial fibrillation is concerned, no significant difference was found between the 2 groups (P >.05). Also, no significant difference was found between operations with cardiopulmonary bypass and beating-heart operations in terms of atrial fibrillation incidence (P >.05). However, atrial fibrillation extended the duration of hospital stay in both groups (P <.05).

CONCLUSION

Our findings indicate that magnesium sulfate infusion alone is not sufficient for the prophylaxis of atrial fibrillation.

[Use of magnesium sulfate in anesthesiology]

The objective of this study was to evaluate usage possibilities of magnesium sulfate in anesthesiology.

METHODOLOGY

In Clinic of Cardiac Surgery, Kaunas University of Medicine magnesium sulfate was started for use as an adjuvant to anesthetics. For anesthesia it was used in 20 cases. This review article presents the methodology based on which the magnesium sulfate anesthesia was given. Methodology was created using the data of international clinical trials. After anesthesia induction with thiopental (5 mg/kg) and fentanyl (2 mg/kg), patients were given shock-dose injection (30-50 mg/kg) of MgSO4; also continual infusion through syringe pump at 500 mg/h was given for total duration of 20 hours. The state of patients during anesthesia was evaluated based on hemodynamic readings: arterial blood pressure, heart rate and functional oxygen saturation in the arterial blood (SpO2).

RESULTS

Data on importance of magnesium sulfate for anesthesia is currently in process, however it was determined that when magnesium sulfate is used for anesthesia, the smaller doses of fentanyl and myorelaxants are needed. The last dose of fentanyl before the end of anesthesia is injected at the similar interval as in cases when magnesium is not used.

CONCLUSIONS

Even though the precise data is not available yet, we can conclude that when magnesium sulfate is used as an adjuvant for anesthesia, the reduced doses of painkiller medicines are needed and their action is strengthened. In addition, magnesium does not prolong the activity of painkiller substances.

Association between maternal serum ionized magnesium levels at delivery and neonatal intraventricular hemorrhage

OBJECTIVES

To determine whether magnesium sulfate (MgSO(4)) exposure is associated with a reduced risk for neonatal intraventricular hemorrhage (IVH).

STUDY DESIGN

In a randomized, controlled trial, women in preterm labor were randomly assigned to receive MgSO(4), "other" tocolytic, or saline control. At delivery, we collected maternal antecubital and umbilical cord blood for determination of serum ionized magnesium levels. Neonatal IVH was diagnosed by cranial ultrasonogram.

RESULTS

Among 144 infants, 24 were diagnosed with IVH. Using crude intention-to-treat analysis, we found that 18% (13/74) of survivors exposed after birth to MgSO(4) had IVH compared with 16% (11/70) of babies who were not exposed. Infants who had IVH were more likely to have been delivered by mothers with higher serum ionized magnesium (Mg) levels (0.75 vs 0.56 mmol/L) (P =.01). Using multivariable logistic regression, we confirmed that higher Mg levels are a significant predictor of neonatal IVH (adjusted odds ratio, 15.8; 95% CI, 1.4-175.0) even when adjusted for birth weight, gestational age, antenatal hemorrhage, and neonatal glucocorticoid exposure.

CONCLUSIONS

In mothers with preterm labor, our data indicate that antenatal MgSO(4) exposure may be associated with an increased risk for IVH among their newborns.

Comparative antithrombotic effects of magnesium sulfate and the platelet glycoprotein IIb/IIIa inhibitors tirofiban and eptifibatide in a canine model of stent thrombosis

BACKGROUND

Antithrombotic effects of glycoprotein IIb/IIIa inhibitors and magnesium are known, but their comparative effects on stent thrombosis are not known. Our objective was to compare the antithrombotic effects of the glycoprotein IIb/IIIa inhibitors tirofiban and eptifibatide with magnesium in an ex vivo canine arteriovenous shunt model of stent thrombosis.

METHODS AND RESULTS

Control nitinol stents were expanded to 2 mm in diameter in a tubular perfusion chamber interposed in the shunt and exposed to flowing arterial blood at a shear rate of 2100 s(-1) for 20 minutes (n=398 perfusion runs in 24 experiments in 8 dogs). The animals were treated intravenously with MgSO4 (2 g bolus x 20 minutes followed by 2 g/h infusion), eptifibatide (double bolus of 180 microg/kg 10 minutes apart followed by 2 microg/kg per minute), or tirofiban (0.3 microg/kg per minute), with or without heparin (50 U/kg). Effects of the test agents on thrombus weight, platelet aggregation (PA), platelet CD62 expression, bleeding time (BT), heart rate, and mean arterial blood pressure were assessed. Treatment with Mg+heparin reduced stent thrombus weight by 78+/-10% compared with baseline (19+/-4 mg, P<0.001). The antithrombotic effect of Mg+heparin was equivalent to that observed with tirofiban+heparin (78+/-13%) and eptifibatide+heparin (84+/-11%). Magnesium had no significant effect on PA and BT. Tirofiban and eptifibatide inhibited PA by >90% and prolonged BT up to 20 minutes. None of the test agents had effects on CD62 expression or activated clotting time. There were no significant bleeding or hemodynamic complications.

CONCLUSION

Magnesium produced a significant reduction in acute stent thrombus formation that was equivalent in magnitude to that produced by clinically relevant doses of tirofiban and eptifibatide. Its potential use in percutaneous coronary intervention requires further study.

Magnesium sulfate attenuates increased blood-brain barrier permeability during insulin-induced hypoglycemia in rats

Magnesium probably protects brain tissue against the effects of cerebral ischemia, brain injury and stroke through its actions as a calcium antagonist and inhibitor of excitatory amino acids. The effects of magnesium sulfate on cerebrovascular permeability to a dye, Evans blue, were studied during insulin-induced hypoglycemia with hypothermia in rats. Hypoglycemia was induced by an intramuscular injection of insulin. After giving insulin, each animal received MgSO4 (270 mg/kg) ip, followed by a 27 mg/kg dose every 20 min for 2.5 h. Plasma glucose and Mg2+ levels of animals were measured. Magnesium concentrations increased in the serum following MgSO4 administration (6.05+/-0.57 vs. 2.58+/-0.14 mg/dL in the Mg2+ group, and 7.14+/-0.42 vs. 2.78+/-0.06 mg/dL in the insulin + Mg2+ group, P < 0.01). Plasma glucose levels decreased following hypoglycemia (4+/-0.66 vs. 118+/-2.23 mg/dL in the insulin group, and 7+/-1.59 vs. 118+/-4.84 mg/dL in the insulin + Mg2+ group, P < 0.01). Blood-brain barrier permeability to Evans blue considerably increased in hypoglycemic rats (P < 0.01). In contrast, blood-brain barrier permeability to Evans blue was significantly reduced in treatment of hypoglycemic rats with MgSO4 (P < 0.01). These results indicate that Mg2+ greatly reduced the passage of exogenous vascular tracer bound to albumin into the brain during hypoglycemia with hypothermia. Mg2+ could have protective effects on blood-brain barrier permeability against insulin-induced hypoglycemia.

Usefulness of magnesium sulfate in stabilizing cardiac repolarization in heart failure secondary to ischemic cardiomyopathy

Experimental heart failure is associated with cardiac magnesium loss, causing increased beat-to-beat variability in the action potential. Unstable repolarization contributes to sudden death, but no therapy has been shown to reduce repolarization variability safely. We sought to test whether a prolonged infusion of magnesium sulfate (MgSO(4); 40 mmol/24 hours) would normalize QT interval variability in patients with compensated heart failure. Fifteen patients (New York Heart Association class II to III; mean age 63 years) were enrolled in a placebo-controlled, double-blind study. Surface electrocardiograms were recorded and digitized at entry and at 48 and 168 hours (drug washout). Repolarization stability was assessed using an automated method measuring each QT interval in a 5-minute epoch. The QT variability index was derived as the ratio of normalized QT-to-normalized heart rate variability. Seven of 15 patients received MgSO(4). Mean heart rate and QT did not change in either group. The QT variability index was stable in the placebo group (-0.69 +/- 0.15 at entry, -0.71 +/- 0.22 at 48 hours, -0.70 +/- 0.18 at 168 hours), but decreased significantly in the treated group at 48 hours (-0.95 +/- 0.19 to -1.36 +/- 0.13, p <0.05 repeated-measures analysis of variance), returning to baseline at 168 hours (-0.84 +/- 0.18). Regression analyses showed that administration of MgSO(4) resulted in a stronger correlation between the QT and RR interval (p <0.01). Thus, MgSO(4) stabilizes cardiac repolarization in patients with compensated heart failure due to ischemic heart disease. Magnesium therapy may be useful in altering the proarrhythmic substrate in heart failure.

Intravenous magnesium sulfate for bronchial hyperreactivity: a randomized, controlled, double-blind study

BACKGROUND

Magnesium has been shown to be helpful in the treatment of acute exacerbations of asthma. Conflicting data exist concerning the effect of magnesium on bronchial hyperreactivity.

METHODS

We performed a randomized, double-blind, placebo-controlled study to investigate the effect of intravenous magnesium sulfate on bronchial reactivity to metacholine in 30 subjects with bronchial hyperreactivity. Two days after baseline metacholine provocation, 20 subjects received 0.3 mmol/kg/h of intravenous magnesium sulfate and 10 subjects received normal saline solution. Metacholine provocation was repeated 30 minutes after the initiation of the magnesium or placebo infusion.

RESULTS

The difference of the postinterventional minus the baseline provocative dose of metacholine required to decrease the forced expiratory volume in 1 second by 20% (PC20) was significantly higher in the magnesium group compared with the placebo group (0.48 +/- 0.46 mg/mL versus 0.05 +/- 0.73 mg/mL, P = .028). In the magnesium group, the PC(20) significantly increased (from 0.83 +/- 0.54 mg/mL to 1.31 +/- 0.66 mg/mL, P = .0001), whereas there was no change in the placebo group (0.86 +/- 0.52 mg/mL to 0.91 +/- 0.54 mg/mL, P = .83).

CONCLUSIONS

In the magnesium group, 30% of the subjects reached a normal PC(20) compared with 10% in the placebo group. We conclude that intravenous magnesium sulfate significantly improved bronchial hyperreactivity and may serve as an adjunct to standard treatment.

Spasmolytic effect of magnesium sulfate on serotonin-induced pulmonary hypertension and bronchoconstriction in dogs

BACKGROUND

Magnesium (Mg2+) has relaxant effects on histamine-induced bronchoconstriction. In addition, Mg2+ has been reported to reduce vascular smooth muscle tone and be clinically useful for treatment of persistent pulmonary hypertension of the newborn. In this study, we evaluated the relaxant effect of Mg2+ on serotonin (5HT)-induced bronchoconstriction and pulmonary hypertension.

METHODS

Seven mongrel dogs were anesthetized with pentobarbital (30 mg x kg(-1) + 2 mg x kg(-1) x h(-1)) and paralyzed by pancuronium (0.2 mg x kg(-1) x h(-1)). Bronchoconstriction and pulmonary hypertension were elicited with 5HT (10 microg x kg(-1) + 1 mg x kg(-1) x h(-1)). Airway caliber was evaluated by changes in bronchial cross-sectional area (BCA) of the 3rd bronchial bifurcation measured by a fiberoptic bronchoscope method as previously reported. Pulmonary hypertension was assessed by changes in pulmonary vascular resistance (PVR). The BCA and PVR were expressed as per cent of the basal level. Thirty minutes after start of 5HT infusion, magnesium sulfate (MgSO4): 0 (saline), 1, 10, 100 and 1000 micromol x kg(-1) was given i.v.. Arterial blood was also collected to measure plasma level of Mg2+ and catecholamines.

RESULTS

5HT increased %PVR to 163+/-25% and decreased % BCA by 39.2+/-4.5%. Plasma level of Mg2+ following MgSO4 1000 micromol x kg(-1) i.v. exceeded its toxic level. The ED50s of MgSO4 (dose producing 50% relaxation of maximal constriction) was 47.8 micromol x kg(-1) and 1.09 mmol x kg(-1) for pulmonary hypertension and bronchoconstriction, respectively. The ratio of %PVR to %SVR was about 1.0 after MgSO4 0-100 micromol x kg(-1) i.v., although the ratio significantly increased after 1000 micromol x kg(-1) i.v..

CONCLUSION

In dogs, 5HT-induced pulmonary hypertension but not bronchoconstriction was significantly reduced by an iv bolus of MgSO4, resulting in a plasma concentration within the assumed therapeutic level.

[Subcutaneous magnesium pump in a patient with combined magnesium transport defect]

HISTORY AND ADMISSION FINDINGS

A 28-year-old man, known to have abnormal intestinal magnesium absorption, presented with recurrent cerebral seizures. Despite daily intravenous sulphate infusions, magnesium concentration remained inadequate. Physical examination was unremarkable.

INVESTIGATIONS

Serum magnesium concentration was markedly reduced to 0.48 mmol/l. The parenteral magnesium tolerance test indicated reduced enteric magnesium absorption of < 20%. Absolute magnesium concentration in 24-hour urine was normal at 6.3 mmol/24 h, but high in proportion to the hypomagnesaemia. All other laboratory data were within normal limits.

TREATMENT AND COURSE

In addition to the known intestinal malabsorption the patient also had isolated renal loss of magnesium. It was only by continuous magnesium infusion with a recently developed portable subcutaneous pump system that normal serum magnesium concentrations were attained and all symptoms disappeared.

CONCLUSION

This patient has combined magnesium transport defects, which could not be effectively treated by conventional methods, but required continuous magnesium infusion with an indwelling subcutaneous infusion pump. This case serves as an example of the way in which subcutaneous infusion can provide physiological substitution of electrolytes.

The effect of magnesium sulfate on fetal heart rate parameters: A randomized, placebo-controlled trial

OBJECTIVE

We sought to determine the effect of magnesium sulfate on fetal heart rate baseline value, variability, and acceleration-deceleration pattern.

STUDY DESIGN

Normal, nonlaboring pregnant patients at >30 weeks' gestation were recruited. Baseline fetal heart rate monitoring for 1 hour was performed. After an 800-kcal meal, patients were randomized to receive either an intravenous loading dose of 6 g of magnesium sulfate in 100 mL of isotonic sodium chloride solution or 100 mL of isotonic sodium chloride solution alone. Subsequently, patients in the magnesium sulfate group received a 2-g/h intravenous infusion for 3 hours at a rate of 125 mL/h. Patients randomized to the sodium chloride solution group received a sodium chloride solution infusion at a similar rate (unlabeled intravenous bags). Maternal blood was drawn at 0, 1, and 3 hours for determination of total and ionized magnesium and calcium, electrolyte, and glucose levels. One hour of fetal heart rate monitoring was repeated at 1 and 3 hours of infusion. Tracings were interpreted without identifiers (of time or group) by using the National Institute of Child Health and Human Development fetal heart rate monitoring guidelines.

RESULTS

Magnesium sulfate administration resulted in decreased fetal heart rate baseline values and variability in the third hour. The fetal heart rate baseline value was 134.4 +/- 6.3 versus 136.6 +/- 6.4 beats/min before infusion (P >.05), 134.4 +/- 7.1 versus 135.1 +/- 6. 6 beats/min in the first hour (P >.05), and 134.6 +/- 7.1 versus 132. 3 +/- 7.6 beats/min in the third hour (P <.05) in the sodium chloride solution group versus the magnesium sulfate group, respectively. Fetal heart rate variability (grades 1-5) was 2.75 +/- 0.33 versus 2.82 +/- 0.29 before infusion (P >.05), 2.81 +/- 0.30 versus 2.84 +/- 0.28 in the first hour (P >.05), and 2.71 +/- 0.52 versus 2.67 +/- 0.36 in the third hour in the sodium chloride solution group versus the magnesium sulfate group, respectively (P <. 05). Magnesium sulfate blocked the positive correlation between gestational age and number of accelerations found in control subjects. No significant decelerations were identified.

CONCLUSIONS

Prolonged administration of magnesium sulfate was associated with decreased fetal heart rate baseline values and variability. Given the small magnitude of these changes, the clinical significance of these findings is questionable. Magnesium sulfate inhibition of the increasing number of accelerations with gestational age needs to be considered when fetal well-being is assessed.

The effect of ionised magnesium on coagulation using thromboelastography

Magnesium is an ionised mineral with therapeutic uses. There is laboratory evidence that it may have an anticoagulant activity although recent research has been to the contrary. The clinical implications of the effect of a therapeutic dose of magnesium on coagulation have yet to be resolved conclusively. In our study, 10 healthy volunteers were given 4 g of magnesium sulphate intravenously. Thromboelastographs were recorded and blood analysed for haematological indices, before and after the infusion. All variables associated with coagulation remained unchanged except the alpha angle on the thromboelastograph which increased significantly. We conclude that in our in vivo study, the effect of magnesium sulphate on coagulation is not clinically significant.

Acute hypermagnesemia and respiratory arrest following infusion of MgSO4 for tocolysis

Hypermagnesemia (6.95 mmol/l) and respiratory arrest occurred to a 20-year-old female (G3P2002) at 26 weeks of gestation during tocolytic treatment with MgSO4.7H2O (density greater than plasmalyte) injected into an i.v. infusion bag containing 1 l of plasmalyte without mixing. The patient was rescued with calcium gluconate and normal pregnancy continued. It is important to adequately mix an i.v. solution after adding a drug particularly when the drug-containing solution has greater density than the parent i.v. solution.

Antinociceptive potentiation and attenuation of tolerance by intrathecal co-infusion of magnesium sulfate and morphine in rats

N-methyl-D-aspartate (NMDA) antagonists, such as MK801, delay the development of morphine tolerance. Magnesium, a noncompetitive NMDA antagonist, reduces postoperative morphine requirements. The present study was designed to evaluate the effects of intrathecal co-administration of magnesium sulfate with morphine on antinociceptive potentiation, tolerance, and naloxone-induced withdrawal signs. Magnesium sulfate (40-60 microg/h) co-administration for 7 days, similar to MK801 (10 nmol/h), prevented the decline in antinociceptive response compared with morphine (20 nmol/h). Magnesium sulfate (60 microg/h) produced no antinociception, but co-infused with morphine (1 nmol/h), it resulted in potentiated antinociception compared with morphine throughout the 7-day period. Probe morphine doses after 7-day infusions demonstrated a significantly greater 50% effective dose value for morphine 1 nmol/h (109.7 nmol) compared with saline (10.9 nmol), magnesium sulfate 60 microg/h (10.9 nmol), and magnesium sulfate 60 microg/h plus morphine 1 nmol/h (11.2 nmol), which indicates that magnesium had delayed morphine tolerance. Morphine withdrawal signs after naloxone administration were not altered by the co-infusion of magnesium sulfate. Cerebrospinal fluid magnesium levels after intrathecal magnesium sulfate (60 microg/h) for 2 days increased from 17.0 +/- 1.0 microg/mL to 41.4 +/- 23.6 microg/mL, although serum levels were unchanged. This study demonstrates antinociceptive potentiation and delay in the development of morphine tolerance by the intrathecal coinfusion of magnesium sulfate and morphine in the rat.

IMPLICATIONS

The addition of magnesium sulfate, an N-methyl-D-aspartate antagonist, to morphine in an intrathecal infusion provided better analgesia than morphine alone in normal rats. These results suggest that intrathecal administration of magnesium sulfate may be a useful adjunct to spinal morphine analgesia.

Magnesium sulfate in labor and risk of neonatal brain lesions and cerebral palsy in low birth weight infants. The Neonatal Brain Hemorrhage Study Analysis Group

OBJECTIVES

We tested the hypothesis that administration of magnesium sulfate in labor protects against the development of neonatal brain lesions and cerebral palsy (CP) in low birth weight infants.

METHODS

Magnesium exposure was ascertained in a population-based cohort of 1105 infants weighing 2000 g or less through review of medical records of maternal magnesium sulfate administration and, where available, elevated maternal serum magnesium levels. Neonatal germinal matrix/intraventricular hemorrhage and parenchymal brain lesions were ascertained by a prospective, timed ultrasound scanning protocol in the first week of life. CP was ascertained at 2 years of age by clinical examination in 80% of survivors and by interview and medical record review in another 6% and was classified as disabling or nondisabling.

RESULTS

No significant reduction in risk of nondisabling CP (adjusted odds ratio [OR], 1.00; 95% confidence interval [CI], 0.53 to 1.88) or disabling CP [DCP] (adjusted OR, 0.63; 95% CI, 0.32 to 1.24) CP with magnesium exposure was found in a logistic regression model that controlled for gestational age, fetal growth, gender, multiple birth status, mode of delivery, amnionitis, and hypertensive disorders. In a small subset of infants, those with onset of parenchymal lesions at 7 days of age or later (n = 29), magnesium exposure was associated with a significantly reduced risk of DCP (OR, 0.10; 95% CI, 0.02 to 0.65). Magnesium sulfate exposure was not associated with germinal matrix/intraventricular hemorrhage (adjusted OR, 0.89; 95% CI, 0.64 to 1.25) or with parenchymal brain lesions (adjusted OR, 0.83; 95% CI, 0.53 to 1.30).

CONCLUSIONS

The hypothesis that magnesium sulfate use reduces the risk of neonatal brain lesions or CP in low birth weight infants was not statistically supported in this study, although a modest reduction in risk of DCP cannot be excluded. The data further suggest that magnesium exposure may be associated with reduction in risk of CP in low birth weight infants who have late-onset brain lesions, but this unpredicted observation requires confirmation in another data set.

Functional magnesium deficiency in critically ill patients identified using a magnesium-loading test

OBJECTIVE

To determine the feasibility of the magnesium-loading test in the critically ill and to validate serum ionized magnesium assay using the magnesium-loading test as a reference in this same patient population.

DESIGN

Double-blind, randomized, controlled clinical investigation.

SETTING

Tertiary level intensive care unit.

PATIENTS

Forty-four consecutive critically ill patients without evidence of renal insufficiency.

INTERVENTION

Patients were randomly allocated to receive 30 mmol (7.5 g) of magnesium sulfate daily for 3 days, or an equivalent amount of normal saline.

MEASUREMENTS AND MAIN RESULTS

We recorded baseline characteristics, and serial serum biochemical measurements included creatinine, glucose, sodium, potassium, phosphate, total calcium, ionized calcium, total magnesium, and ionized magnesium. Serum assays were accompanied by 24-hr urine collections of creatinine and magnesium over the 3-day period. Baseline characteristics were comparable in both groups. In patients receiving magnesium, serum ionized magnesium and total magnesium concentrations were increased by 43% (p = .0001) and 59% (p = .0002), respectively, on day 1 as compared with the control group. Magnesium excretion in the control group averaged 4.8 +/- 2.3 mmol/day during the 3-day study period, while the magnesium excretion in the magnesium-loaded group was significantly increased to 22.7 +/- 10.9 mmol/day (p < .0001). Following day 1 magnesium loading, patients who excreted < 70% of the total magnesium (30 mmol infused magnesium plus 4.8 mmol basal excretion) were termed as functionally magnesium-deficient retainers (n = 12), and patients who excreted > 70% of the total magnesium were termed as nonretainers (n = 7). In addition, magnesium retainers on day 2 (nine of ten patients) and day 3 (five of six patients) excreted > 70% of the total magnesium, indicating a replenishment of body magnesium stores. In contrast, nonretainers on day 2 (four of five patients), and day 3 (four of four patients) continued to excrete excess amounts of magnesium. In the retainer group, only two patients had a low serum ionized magnesium concentration, while two other patients had low total serum magnesium values. In addition, magnesium retention was associated with low ionized calcium and high phosphate values.

CONCLUSIONS

The magnesium-loading test is feasible and appears to be valid based on its performance during the 3-day evaluation. Using the magnesium-loading test as a reference, serum ionized magnesium appears to be an insensitive biochemical marker of functional hypomagnesemia. Larger cohort studies using the magnesium-loading test will help establish the true prevalence of magnesium deficiency and its associated risk factors in critically ill patients.

The effects of plasma and brain magnesium concentrations on lidocaine-induced seizures in the rat

Lidocaine and MgSO4 are often coadministered to patients with pregnancy-induced hypertension. This study examined whether MgSO4 alters the lidocaine-seizure threshold in the rat and, if so, whether systemic MgSO4 administration is as effective as intracerebroventricular MgSO4 infusion. In Experiment 1, rats were administered 50% MgSO4 or 0.9% NaCl intravenously (IV) (20 microL/h) for 5 days. In Experiment 2, rats were administered 0.9% NaCl, 0.8% MgSO4, or 2.0% MgSO4 (10 microL/h) via intracerebroventricular infusion for 24 h. All rats then underwent continuous IV lidocaine infusion until onset of electroencephalographic seizures. In Experiment 1, plasma [Mg2+] was greater in the MgSO4 group (5.1 +/- 1.5 mg/dL vs 1.8 +/- 0.3 mg/dL) but neither the dose of lidocaine required to induce seizures (MgSO4 = 19 +/- 2 mg/kg; saline = 23 +/- 5 mg/kg) nor brain [Mg2+] (MgSO4 = 794 +/- 17 micrograms/g; saline = 788 +/- 33 micrograms/g) were changed. In Experiment 2, intracerebroventricular MgSO4 increased both brain [Mg2+] (2% MgSO4 = 923 +/- 79 micrograms/g; saline = 788 +/- 35 micrograms/g) and the lidocaine seizure dose (2% MgSO4 = 39 +/- 7 mg/kg; saline = 26 +/- 3 mg/kg). Although intracerebroventricular administration of MgSO4 produces an anticonvulsant effect, chronic hypermagnesemia does not alter whole brain [Mg2+] and therefore offers no protection from lidocaine-induced seizures in this model.

Role of magnesium sulfate in postoperative analgesia

BACKGROUND

N-methyl-D-aspartate antagonists may play a role in the prevention of pain. An assessment was made of the effect of the physiologic N-methyl-D-aspartate antagonist magnesium on analgesic requirements, pain, comfort, and quality of sleep in the postoperative period.

METHODS

In a randomized, double-blind study, 42 patients undergoing elective abdominal hysterectomy with general anesthesia received 20% magnesium sulfate or saline (control) 15 ml intravenously before start of surgery and 2.5 ml/h for the next 20 h. Postoperative morphine requirement was assessed for 48 h using patient-controlled analgesia. Maximum expiratory flow (peak flow), pain at rest and during peak flow, and discomfort were evaluated up to the 48th postoperative hour, and 1 week and 1 month after surgery. Insomnia was evaluated after the first and second postoperative nights.

RESULTS

Compared to control subjects, magnesium-treated patients consumed less morphine during the first 48h (P<0.03), which was most pronounced during the first 6 h (P<0.004), and experienced less discomfort during the first and second postoperative days (P<0.05-0.005). The magnesium-treated group revealed no change in postoperative sleeping patterns when compared to preoperative patterns. Control patients showed an increase in insomnia during the first and second postoperative nights (P<0.002 and P<0.005, respectively) compared to preoperative values.

CONCLUSIONS

This is the first clinical study showing that the perioperative application of magnesium sulfate is associated with smaller analgesic requirement, less discomfort, and a better quality of sleep in the postoperative period but not with adverse effects. Magnesium could be of interest as an adjuvant to postoperative analgesia.

A comparison of serum magnesium sulfate levels in pregnant women with severe preeclampsia between intravenous and intramuscular magnesium sulfate regimens: a randomized controlled trial

The frequency of blood samples that achieved therapeutic level was lower in the group of maintenance with intravenous regimen than the intramuscular regimen significantly at 15, 30, 60, 120 and 240 minutes after loading dose. The mean level of serum magnesium sulfate in the intravenous group was significantly lower than intramuscular group. This study supported to choose the maintenance by intramuscular regimen. However, further study is required to analyse the effect of higher level of magnesium sulfate in Thai patients.

Hypermagnesemia following an acute ingestion of Epsom salt in a patient with normal renal function

CASE REPORT

Hypermagnesemia is a rare condition that commonly follows excessive therapeutic administration of magnesium sulfate to treat eclampsia of pregnancy. Signs and symptoms of this condition include extreme muscle weakness, loss of deep tendon reflexes, mental status depression, and cardiac dysrhythmias. Clinically significant hypermagnesemia following oral or rectal administration of magnesium containing products in patients with normal renal function is rare. We report a case of hypermagnesemia following massive Epsom salt ingestion that resulted in extreme musculoskeletal weakness and altered mentation.

Magnesium repletion and its effect on potassium homeostasis in critically ill adults: results of a double-blind, randomized, controlled trial

OBJECTIVES

The aims of this study were to evaluate the safety and efficacy of magnesium replacement therapy and to determine its effect on potassium retention in hypokalemic, critically ill patients.

DESIGN

A prospective, double-blind, randomized, placebo-controlled trial.

SETTING

A surgical intensive care unit (ICU).

PATIENTS

A total of 32 adult surgical ICU patients were admitted to the study on the basis of documented hypokalemia (potassium of < 3.5 mmol/L) within the 24-hr period before entering the study. Patients were randomized to receive either placebo (n = 15) or magnesium sulfate (n = 17). One patient from each group was excluded from the study due to failure to complete the full series of doses.

INTERVENTIONS

Patients received a "test dose" of either magnesium sulfate (2 g, 8 mmol) or placebo (5% dextrose in water) infused over 30 mins every 6 hrs for eight doses. The next schedule test dose was held if hypermagnesemia (magnesium of > 2.8 mg/dL [> 1.15 mmol/L]) was documented at any time during the study. Routine replacements of potassium and magnesium continued during the duration of the study, when clinically indicated, for serum potassium concentrations of 3.5 mmol/L or serum magnesium concentrations of < 1.8 mg/dL (< 0.74 mmol/L).

MEASUREMENTS AND MAIN RESULTS

Age, weight, and Acute Physiology and Chronic Health Evaluation II scores were recorded on entry into the study. Just before administration of each test dose, blood was drawn for magnesium and potassium, bicarbonate, pH, and glucose determinations, and an aliquot of the preceding 6 hrs urine collection was sent for magnesium and potassium determinations. Serum calcium, phosphate, urea nitrogen, and creatinine concentrations were measured daily. The amounts of magnesium and potassium administered via parenteral nutrition, tube feeding, and replacement infusions were calculated for each 6-hr interval. The amounts of magnesium and potassium excreted in the urine were similarly assessed. The groups showed no differences with regard to age, weight, Acute Physiology and Chronic Health Evaluation II scores, or initial serum magnesium concentration. Initial potassium, bicarbonate, pH, calcium, phosphate, glucose, blood urea nitrogen, and creatinine values were not different between groups. Patients receiving magnesium sulfate showed a statistically significant increase in serum magnesium concentration at 6 hrs when compared with placebo, as well as with itself at time 0 (p < .0001), a difference maintained throughout the study. Compared with the placebo group, the total amount of elemental magnesium administered was significantly greater in the treatment group (1603 +/- 124 vs. 752 +/- 215 mg [65.7 +/- 5.8 vs. 30.8 +/- 8.8 mmol], p < .0001), as was urine magnesium excretion (1000 +/- 156 vs. 541 +/- 68 mg [41.0 +/- 6.4 vs. 22.2 +/- 2.8 mmol] p < .0001). However, the net magnesium balance (total magnesium in - total urine magnesium) was significantly more positive in the treatment group (612 +/- 180 vs. 216 +/- 217 mg [25.1 +/- 7.4 vs. 8.9 +/- 8.9 mmol], p < .005). The treatment and control groups had the same serum potassium concentrations and did not receive different amounts of potassium (245 +/- 39 vs. 344 +/- 45 mmol, respectively, p = .06), although the treatment group required less potassium replacement/6 hrs by 30 hrs compared with itself at time 0 (p < .05). Despite the same serum potassium values, the net potassium balance for 48 hrs was positive in the treatment group (+ 72 +/- 32 mmol) and negative in the control group (-74 +/- 95 mmol, p < .05). There were no complications associated with the magnesium sulfate administration.

CONCLUSIONS

Magnesium sulfate administered according to the above regimen safety and significantly increases the circulating magnesium concentration. Despite greater urine magnesium losses in the treatment group, this group exhibited significantly better magnesium retention.

Effective use of magnesium for acquired torsade de pointes in a 4-month-old infant

We report a 4-month-old infant with torsade de pointes secondary to procainamide treatment. The infant presented with atrial flutter and converted to normal sinus rhythm with intravenous procainamide. Oral procainamide therapy was initiated as the infusion was tapered, and the patient subsequently developed incessant torsade de pointes. Once the proarrhythmia was recognized, procainamide was withheld, and intravenous magnesium was administered. The torsade de pointes resolved after one bolus of magnesium sulfate. An infusion regimen of magnesium was given until the procainamide and N-acetylprocainamide concentrations became undetectable. Intravenous magnesium should be administered to newborns with acquired torsade de pointes; dosing guidelines for its use are suggested.

Action of MgSO4 differs from moricizine and verapamil on ouabain-induced ventricular tachycardia in normomagnesemic conscious dogs

We performed a comparative study to determine whether acute administration of MgSO4, moricizine, and verapamil to conscious dogs with normal plasma magnesium levels (0.75 +/- 0.06 mM) terminates ouabain-induced ventricular tachycardia (VT). This arrhythmia is dependent on triggered activity (TA) resulting from delayed afterdepolarizations (DADs). In animals with surgically induced complete atrioventricular (AV) block, monomorphic VT was induced by programmed ventricular stimulation during continuous intravenous (i.v.) infusion of ouabain. At the moment of drug administration, VT persisted for at least 20 min, while the rate was stable for at least 5 min. A single dose of MgSO4 (100 mg/kg i.v.) abolished only VTs with cycle lengths > or = 320 ms (335 +/- 10 ms); VTs with faster cycle lengths (300 +/- 20 ms) were merely slowed, although the increase in plasma magnesium levels was considerable and comparable in both groups (3.9 +/- 1.6 and 4.8 +/- 1.9 mM). In contrast, moricizine (2 mg/kg i.v.) and verapamil (0.5-1.0 mg/kg i.v.) terminated both fast and slow VTs. The cycle length of VT ranged from 280 to 320 ms (mean 300 +/- 15 ms) for moricizine and 260-330 ms (mean 300 +/- 25 ms) for verapamil.(ABSTRACT TRUNCATED AT 250 WORDS)

[Cardiorespiratory and electrolytic changes in status asthmaticus after intravenous administration of magnesium sulfate]

The authors studied cardiorespiratory effects of MgSO4 infusion in 30 randomized patients with status asthmaticus. They found, that after having the drug administered, values of VC, FEV1, FIV1, PaO2 and pH increased, the respiratory and heart rate, diastolic blood pressure reduced. Other ventilation, blood gas and ECG parameters were unchanged. Among the electrolytes, serum Ca2+ level has reduced, both plasma and intracellular Mg2+ concentrations increased. It is apparent from the results, that broncholytical ability of MgSO4 given in therapeutical dose i.v. does not reach the level of beta-stimulating agents. However, this completed with the cardioprotective, sedative effect as well as more advantageous ion-distribution, influences favourably the asthmatic dyspnoea.

Effect of magnesium sulfate on the vascular actions of norepinephrine and angiotensin II

Magnesium sulfate is used for seizure prophylaxis in patients with preeclampsia. It also has significant effects on calcium metabolism and could, therefore, alter the pressor response to calcium-dependent vasoconstrictors. The present in vivo rat study examined the effect of magnesium sulfate to alter the pressor response to norepinephrine (NE) and angiotensin II (A II). Magnesium doses were chosen to approximate those used in treating preeclampsia. NE resulted in a significant rise in mean arterial pressure (delta MAP, 46 +/- 3.7 mmHg; p < 0.001). A II also resulted in a significant rise in MAP (delta MAP, 23 +/- 3.6 mmHg, p < 0.02). Magnesium sulfate alone had no significant effect on MAP but attenuated the pressor response to both NE (delta MAP, 16 +/- 1.5 mmHg) and A II (delta MAP, 12 +/- 2.5 mmHg). After discontinuation of the magnesium sulfate infusion, the control pressor responses to NE and A II were again seen (delta MAP, 39 +/- 3.5 mmHg and delta MAP, 28 +/- 4.2 mmHg, respectively). Although magnesium sulfate is not a primary antihypertensive agent, it may have effects on blood pressure by attenuating the actions of circulating vasoconstrictors.

Intravenous magnesium sulphate in suspected acute myocardial infarction: results of the second Leicester Intravenous Magnesium Intervention Trial (LIMIT-2)

The cardiovascular actions of the magnesium ion at pharmacological concentrations include coronary and systemic vasodilatation, platelet inhibition, and antiarrhythmic effects. Magnesium has also been reported to protect myocardial tissue in experimental models of ischaemia and reperfusion. Several small clinical trials in suspected acute myocardial infarction have suggested that early mortality can be reduced by intravenous infusion of magnesium salts in the acute phase, but none has been of sufficient size to be conclusive. We therefore conducted a randomised, double blind, placebo controlled study in 2316 patients with suspected acute myocardial infarction who received either intravenous magnesium sulphate (8 mmol over 5 min followed by 65 mmol over 24 h) or physiological saline. The primary outcome measure was 28-day mortality, which was ascertained in 99.3% of patients. The groups were well balanced for prognostic factors. By intention-to-treat analysis mortality from all causes was 7.8% in the magnesium group and 10.3% in the placebo group (2p = 0.04), a relative reduction of 24% (95% confidence interval 1-43%). Within the coronary care unit the incidence of left ventricular failure was reduced by 25% (7-39%) in the magnesium group (2p = 0.009). There was no significant difference between the groups in the incidence of heart block or the use of antiarrhythmic drugs, direct-current cardioversion, or temporary pacing. Myocardial infarction was confirmed in 65% of each group, with closely similar rises in cardiac enzymes. The side-effects of magnesium treatment were transient flushing, related to speed of injection of the loading dose, and an increased incidence of sinus bradycardia (2p = 0.02). Exploratory subgroup analyses of 28-day mortality did not indicate any effect modification by thrombolysis or aspirin, or by previous treatment with beta blockers, calcium antagonists, or diuretics. Intravenous magnesium sulphate is a simple, safe, and widely applicable treatment. Its efficacy in reducing early mortality of myocardial infarction is comparable to, but independent of, that of thrombolytic or antiplatelet therapy.