Pros and cons of magnesium sulfate as a tocolytic

Magnesium sulphate (MgSO4) is with a proved effectiveness in cases of praeclampsia/eclampsia, but its use as a tocolytic is discussed in the last few years. That is why we had for an object to study its effect as a tocolytic in cases of abortions and premature labours. The study is prospective and if is made in I-st obstetric clinic of High Medical School--Pleven. Treatment with Cormagnesin was carried out to pregnant women for suppressing the uterine activity. Cormagnesin 200 (1 amp-10 ml) contains 1000 mg MgSO4, and Cormagnesin 400 (1 amp-10 ml) contains 2000 mg MgSO4. The medicine was administered in dosage of 4 or 5 g for 30 min, and after that if there were any uterine contractions the infusion was carried on with additional 5 g MgSO4 for 6 to 12 h. The total dosage was from 4 to 60 g MgSO4. The authors reported on very good effect in cases with pains and increased uterine tone--18 (36.73%), as well as in cases with pains and irregular uterine contractions 5 (10.21%), while the treatment was without any effect in cases with uterine contractions on 15-20 min, increased uterine tone, bleeding and Pelvic score 1-3 points in spite of high dosages of MgSO4 and longer duration of treatment. The authors made the conclusion, that the subjective complaints should not be accepted as an indication for administration of MgSO4, and MgSO4 should be administered in cases with increased uterine tone and irregular uterine contractions. Every genital bleeding and suspicion for placental abruption should be defined more precisely, because lately diagnosed placental abruption and unjustified expectation for suppression of uterine activity by MgSO4, may lead to increase of perinatal morbidity and mortality. In spite of the controversial data about MgSO4 as a tocolytic, its administration is justified and necessary.     

Symptomatic hypocalcemia after tocolytic therapy with magnesium sulfate and nifedipine

OBJECTIVES: In this study, we presented 2 cases and evaluated the evidence for symptomatic hypocalcemia after treatment with magnesium sulfate alone or combined with use of nifedipine. STUDY DESIGN: Case reports, such as the one that follows, and literature review were used. A 25-year-old gravida presented at 33 weeks' gestation with advanced preterm labor. She received magnesium sulfate followed by nifedipine and experienced bilateral hand contractures 12 hours after discontinuation of magnesium sulfate. Total serum calcium was 5.4 mg/dL. A 35-year-old gravida presented at 26 weeks' gestation with ruptured membranes and received magnesium sulfate until it was discontinued prematurely because of pulmonary edema. Twenty hours later she experienced bilateral hand contractures; total serum calcium was 5.9 m/dL. Symptoms for both patients resolved with calcium gluconate therapy. RESULTS: Hypocalcemia is a well-recognized complication of magnesium sulfate infusion. These are the fifth and sixth symptomatic case reports, as identified by Medline Search. Our first case is the only report in which the subsequent use of nifedipine may have been a factor. Little has been reported on the possible toxicity associated with the combined or sequential use of magnesium sulfate and nifedipine. CONCLUSION: Marked hypocalcemia is clearly associated with magnesium sulfate infusion, is likely dose related, and may appear after discontinuation of magnesium sulfate therapy. Moreover, while the evidence for synergistic toxicity of magnesium sulfate and nifedipine is sparse, caution is advised when these agents are used together.     

Thermic effects of tocolytic agents: decreased temperature with magnesium sulfate

The effect of the tocolytic agents terbutaline and magnesium sulfate on patients' temperatures was examined. Fifty-two women admitted for preterm labor were randomized to a treatment protocol for one of the two agents. Oral temperatures were measured initially and every two hours during treatment. There was no significant difference between the initial temperature and the lowest temperature recorded during treatment in the terbutaline group, but temperature decreased significantly during treatment with magnesium sulfate. This decrease in maternal temperature may have importance in the treatment of preterm labor with magnesium sulfate in patients with an infectious etiology for uterine activity.     

Evaluation of maternal fluid dynamics during tocolytic therapy with ritodrine hydrochloride and magnesium sulfate.

OBJECTIVE: The purpose of the study was to observe and compare the effects of ritodrine hydrochloride and magnesium sulfate on maternal fluid dynamics. STUDY DESIGN: Fourteen women in preterm labor were prospectively studied during tocolytic therapy with either ritodrine hydrochloride or magnesium sulfate. The cardiovascular and renal effects of a pretreatment crystalloid infusion were compared with those observed during tocolytic therapy. Profile analysis and repeated measures of variance were used to analyze the data. RESULTS: Ritodrine hydrochloride was associated with decreased colloid osmotic pressure, hematocrit, and serum proteins and increased maternal and fetal heart rates. Arginine vasopressin levels increased during the first 2 hours of therapy, then returned to baseline. Sodium excretion was reduced and there was marked fluid retention. Intravenous magnesium sulfate also resulted in a reduction of colloid osmotic pressure, but hematocrit, serum protein concentration, arginine vasopressin, maternal and fetal heart rates, and mean arterial pressure were minimally affected. Sodium excretion increased to a maximum at 6 to 8 hours of treatment, then returned to baseline. A positive fluid balance was also noted in magnesium sulfate-treated patients but to a lesser degree than with ritodrine. CONCLUSIONS: Sodium retention appears to be the primary cause of plasma volume expansion in ritodrine-treated patients, whereas volume expansion during magnesium sulfate therapy is probably related to intravenous overhydration. In the absence of risk factors for pulmonary capillary membrane injury, available evidence supports volume overload as the principal mechanism for pulmonary edema during tocolytic therapy.     

Tocolytic magnesium sulfate toxicity and unexpected neonatal death.

A 31-year-old primigravida with twins had spontaneous rupture of the membranes at 32 weeks' gestation. On admission, because of contractions, the mother was started on tocolytic magnesium sulfate (MgSO4) along with betamethasone and prophylactic antibiotics. About a day later, she was found to have magnesium toxicity. Her serum total magnesium level was 9.0 mg/dl. Tocolysis was immediately discontinued. At cesarean delivery the following day, twin A, a female, died at 30 minutes of age despite a vigorous resuscitation. Although the preceding fetal heart rate patterns had been reassuring and the umbilical blood gases were normal, quite unexpectedly, the Apgar scores were 1/1/0. An autopsy revealed no anatomic abnormalities. Twin B, a female who survived, was also intubated at delivery. During her stay in the Neonatal Intensive Care Unit, she was found to have modestly elevated levels of serum cardiotroponin T. In our opinion, it is probable that the death of twin A can be directly attributed to magnesium sulfate toxicity. Neonatologists who attend deliveries should be aware that unexpected death may occur in babies who were exposed to high doses of tocolytic MgSO4.     

Magnesium sulfate as a tocolytic agent

Although magnesium sulfate is widely used as a tocolytic agent in the hope of preventing spontaneous preterm birth, there is a paucity of data from large well-designed randomized clinical studies demonstrating the efficacy of magnesium sulfate therapy. Given the potential for untoward side effects and the inherent risks of magnesium sulfate therapy, a thorough understanding of the potential risks and benefits of this agent is needed. To accomplish this understanding we have provided a detailed review the history, pharmacology, physiology, maternal/fetal side effects, and tocolytic efficacy of magnesium sulfate.     

Magnesium sulfate as a tocolytic agent

Magnesium sulfate (MgSO4) has been successfully used to inhibit premature labor. A retrospective review was performed on the use of MgSO4 as a tocolytic agent at Memorial Hospital, Long Beach, California, during a 4-year period (1978-1982). Three hundred fifty-five patients with diagnoses of premature labor were treated with MgSO4 after transport from another hospital. Two hundred seventy-four patients (77%) had a singleton pregnancy with intact membranes, 38 (11%) had a singleton pregnancy with ruptured membranes, 35 (10%) had a multiple gestation with intact membranes, and eight (2%) had a multiple gestation with ruptured membranes. Delivery was successfully delayed in the majority of patients, and the incidence of unexplained failure of tocolysis was only 2%. Side effects occurred in 24 patients (7%) and necessitated stopping the drug in only seven (2%). Serum magnesium levels are reported and the use of MgSO4 in patients with significant vaginal bleeding is discussed. MgSO4 was found to be a successful, inexpensive, and relatively nontoxic tocolytic agent that had few side effects.     

Magnesium sulfate: the first-line tocolytic

Magnesium sulfate has become the first-line tocolytic for short-term use to arrest idiopathic preterm labor. The reasons for its acceptance include familiarity of the drug, ease of use, and the virtual absence of serious maternal side effects. Sufficient data exist showing its efficacy if used in higher doses. Attention to treating preterm labor has shifted to seeking answers about the fundamental causes. Gathering information about the specific causes and designing tailor-made treatment protocols for each of the numerous potential causes is essential. Scientifically sound research is needed to obtain answers about the important clinical questions surrounding magnesium sulfate.     

Marked hypocalcemia after tocolytic magnesium sulphate therapy

Symptomatic hypocalcemia has been reported infrequently in association with magnesium sulfate (MgSO (4)) tocolytic therapy. We report a 38-year-old woman who presented in preterm labor at 24 3/7 weeks. Twenty hours after starting MgSO (4), she developed chest pain. Studies revealed therapeutic serum Mg level, total serum calcium (Ca) = 5.5 mg/dL, 24-hour urine Ca = 763.9 mg, and low serum uric acid and phosphate levels. All studies corrected day 1 postpartum; urine Ca level corrected on day 2. Even short courses of MgSO (4) can result in severe hypocalcemia, raising the question of whether Ca levels should be routinely monitored.     

Hypersensitivity to magnesium sulfate

Two patients who were labor and delivery nurses were treated with intravenous magnesium sulfate because of preterm labor. Both patients had a rapid and sudden onset of an urticarial eruption. The eruption cleared when magnesium sulfate was discontinued. The reactions did not affect the mothers or fetuses, but other therapies to stop labor were necessary.     

Comparative study of the effects of two tocolytic agents (magnesium sulfate and alcohol) on the ionic transfer through the isolated human amnion

The effects of two tocolytic agents (MgSO4 and ethanol) on ionic transfer through the isolated human amnion were observed and compared. The ionic transfer was estimated by conductance and ionic flux measurements. MgSO4 increased the ionic conductance (Gt) on the fetal side; it also increased the ionic fluxes from fetus to mother and from mother to fetus, but it decreased the flux ratio. Ethanol decreased Gt in both directions as well as the ionic fluxes; the flux ratio, however, remained constant. Thus, the two tocolytic agents (MgSO4 and ethanol) show a negative effect on ionic transfer through the human amnion.     

Neuromuscular blockade with magnesium sulfate and nifedipine

A patient who received tocolysis with nifedipine developed neuromuscular blockade after 500 mg of magnesium sulfate was administered. This reaction demonstrates that nifedipine can seriously potentiate the toxicity of magnesium. Caution should be exercised when these two tocolytics are combined.