The use of magnesium sulfate as the primary tocolytic agent to prevent premature delivery

A Study on the Association between Low Maternal Serum Magnesium Level and Preterm Labour

Objectives. The study was aimed to assess the association between low maternal serum magnesium levels and preterm labour. Methods. It is a cross-sectional case-control study in which eligible participants were pregnant women admitted in labour within the labour ward complex of a Lagos tertiary hospital. Relevant data were extracted from the case records of these women and blood samples were obtained from all participants and serum magnesium levels measured. Results. The study showed that 36% of the study patients had varying degrees of hypomagnesaemia. The relative risk indicates that preterm labour is 1.83 times higher among the patients with low serum magnesium (less than 1.6 mg/dL). The mean difference in serum magnesium levels in both groups was statistically significant (P<0.05). Conclusion. We can infer that low serum magnesium (hypomagnesaemia) is associated with preterm onset of labour. We can, also from this finding, formulate a proposition that would help in preventing preterm labour and birth with the use of prophylactic oral magnesium supplementation among patients with higher risk for development of preterm labour.

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.

Management options for preterm labour in Canada

OBJECTIVES

(1) To determine the current use of treatment options for preterm labour and (2) to review the relative safety and efficacy of each class of tocolytic agent.

METHODS

MEDLINE and the Cochrane Library were searched using the terms "preterm delivery," "preterm labour," and "tocolysis" alone, and in combination with the terms "betamimetics," "ritodrine," "magnesium sulfate," "calcium channel blockers," "nifedipine," "prostaglandin synthetase inhibitors," "indomethacin," "glyceryl trinitrate," "nitroglycerin," "oxytocin antagonists," and "atosiban." Randomized controlled trials (RCTs) that compared the effect of a tocolytic with a placebo or other tocolytic in women with preterm labour were selected. Trials were assessed according to Jadad's validated quality scale for assessing the quality of RCTs. Thirty two RCTs retrieved met the inclusion criteria. Information not evident from RCTs was sought from non-randomized clinical trials, cohort studies, case control studies, case series, and case reports. Data from the Canadian Survey on Tocolytic Use was obtained directly from the Society of Obstetricians and Gynaecologists of Canada (SOGC).

RESULTS

The available evidence on the use of tocolytics to prolong pregnancy fails to show benefits in neonatal survival and reduced disability. This uncertainty of benefit makes the issue of fetal and maternal drug toxicity more important. There is great concern among SOGC members over the lack of effective and safe treatment options for the management of preterm labour.

CONCLUSIONS

Further well-designed placebo-controlled trials are necessary to study the efficacy and safety of tocolytics in managing preterm labour.

An update on the controversies of tocolytic therapy for the prevention of preterm birth

Preterm birth is the major cause of perinatal mortality and morbidity in the developed world. Where there are no contraindications to their use, tocolytics can improve neonatal survival rates by approximately 3% per day between 23 and 27 weeks gestation with a concomitant reduction in morbidity. The ultimate aim of tocolytic therapy is to prolong pregnancy until growth and maturation is complete, but even short-term delay may enable the administration of antepartum glucocorticoids to reduce hyaline membrane disease or to arrange transfer to a center with neonatal intensive care facilities. Both of these have been shown to reduce neonatal mortality and morbidity. Until recently, none of the currently used tocolytics, whether licensed or unlicensed, were developed specifically for the inhibition of preterm labor and consequently, they exhibit various potentially serious side-effects. As a result of the recent licensing of the oxytocin antagonist, atosiban, developed for the treatment of preterm labor and due to its high utero-specificity, obstetricians have experienced an advance in their options for the management of spontaneous preterm labor.

Antenatal magnesium exposure and neonatal demise

OBJECTIVE

To assess the effect of antenatal magnesium sulfate exposure on neonatal demise.

STUDY DESIGN

A retrospective analysis of prospectively captured data from 100 tertiary centers between May 1997 and January 2000 was performed. Included were nonanomalous newborns who were admitted to the neonatal intensive care unit between 23 and 34 completed weeks' gestation. Predictors of neonatal demise were determined from a pool of 24 candidate variables in a univariate analysis. A multivariate predictive model for mortality was constructed by using the variables that had significant interactions with the rate of demise (P < or = .1).

RESULTS

A total of 12,876 cases were available for analysis. When these cases were stratified according to gestational age, magnesium was associated with a significant reduction in neonatal demise (OR, 0.67; 95% CI, 0.54 to 0.84; P =.0005). The effect remained when controlling for both gestational age and indication for therapy (adjusted OR, 0.70; 95% CI, 0.56 to 0.89; P =.003). The effect was similar in direction and magnitude in the final model after controlling for additional antenatal factors (OR, 0.82; 95% CI, 0.65 to 1.04; P =.108).

CONCLUSION

Antenatal magnesium exposure is not associated with neonatal death, regardless of indication for therapy.

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.

Clinical issues surrounding the use of terbutaline sulfate for preterm labor

beta-mimetics have been prescribed by physicians to arrest or prevent premature labor for more than 20 years. Although not approved by the Food and Drug Administration (FDA) for tocolytic use, terbutaline sulfate has been the most widely prescribed beta-mimetic in the United States. Recently, the role of terbutaline in the treatment and prevention of preterm labor has been questioned by the FDA. Because the off-label use of drugs is a formally accepted practice in medicine when scientific studies support such use, we reviewed the currently available clinical literature on terbutaline use in various routes of delivery: intravenous, oral, and subcutaneous via infusion pump. This review describes the clinical evidence that supports the safe and effective use of terbutaline as a tocolytic agent in certain patient populations. Practicing physicians should continue to have unrestricted use of terbutaline for tocolysis as one of the few remaining therapeutic options remaining in the fight against preterm birth.

Comparison of lytic cocktail and magnesium sulphate regimens in eclampsia: a retrospective analysis

Retrospective analysis of eclamptic patients was done during two time periods. In time period A (Jan. 1987-Dec. 1988), 79 patients of eclampsia were treated with lytic cocktail and in time period B (April 1992-April 1994), 104 eclamptic patients were treated with magnesium sulfate. The severity of disease, details of labour, delivery, incidence of persistent convulsions and the maternal and perinatal outcomes were compared. Incidence of persistent convulsions was significantly lower with magnesium sulphate (4.8%) compared to lytic cocktail (26.6%). No difference was observed in duration of labour and mode of delivery. Perinatal mortality was significantly lower in magnesium sulphate treated group. Maternal mortality was similar in both the groups (lytic cocktail-3.8%, Magnesium sulphate-2.9%).

The effect of magnesium sulfate therapy on the duration of labor in women with mild preeclampsia at term: a randomized, double-blind, placebo-controlled trial

OBJECTIVE

The primary outcome was to determine whether magnesium sulfate therapy prolongs the duration of labor in women with mild preeclampsia. Secondary outcomes were to assess the side effects associated with magnesium sulfate therapy: hours and maximum dose of oxytocin, incidence of progression to severe preeclampsia, incidence of cesarean delivery, change in maternal hematocrit, incidence of postpartum hemorrhage, incidence of maternal infection, and Apgar scores.

STUDY DESIGN

Women with a diagnosis of mild preeclampsia at term were randomized to receive standard therapy during labor and for 12 hours post partum with either magnesium sulfate (n = 67) or a matching placebo solution (n = 68).

RESULTS

There was no difference between magnesium sulfate and placebo with respect to the primary outcome variables: total length of labor (median 17.8 hours vs 16.5 hours, p = 0.7) and length of the active phase of labor (median 5.4 hours vs 6.0 hours, p = 0.5). In addition, no difference was observed in the secondary outcome variables: hours of oxytocin use, change in hematocrit, frequency of maternal infection, progression to severe preeclampsia, incidence of cesarean delivery, and Apgar scores. Although not statistically significant, the incidence of postpartum hemorrhage was approximately fourfold greater in the magnesium sulfate group (relative risk 4.1, 95% confidence interval 0.5 to 35.4). There was a significant difference in the maximum dose of oxytocin used (13.9 +/- 8.6 mU/min with magnesium sulfate vs 11.0 +/- 7.6 mU/min with placebo, p = 0.036).

CONCLUSION

The use of magnesium sulfate during labor in women with mild preeclampsia at term does not affect any component of labor but did necessitate a higher dose of oxytocin.

Does magnesium sulfate affect the length of labor induction in women with pregnancy-associated hypertension?

OBJECTIVE

Our purpose was to determine whether seizure prophylaxis with magnesium sulfate prolongs induction of labor in women with pregnancy-associated hypertension.

STUDY DESIGN

Women with a singleton pregnancy in vertex presentation between 32 and 42 weeks' gestation who required induction of labor for either preeclampsia, preeclampsia superimposed on chronic hypertension, or transient hypertension were randomized to receive either magnesium sulfate or phenytoin (Dilantin) for seizure prophylaxis. Women with rupture of the membranes, spontaneous contractions resulting in cervical change, or an initial cervical examination showing > 2 cm dilatation and 50% effacement were excluded.

RESULTS

Fifty-four women were randomized to receive either magnesium sulfate (n = 28) or phenytoin (n = 26). The two groups were similar for selected maternal antepartum, intrapartum, and postpartum characteristics that have been associated with a prolongation or failure of labor induction. The two groups were also similar for the interval from the start of induction to (1) the first examination > or = 5 cm cervical dilatation and (2) delivery and in the frequency of women requiring cesarean delivery.

CONCLUSION

Compared with phenytoin, magnesium sulfate seizure prophylaxis in women with pregnancy-associated hypertension does not prolong the induction of labor nor does it result in an increase in cesarean deliveries.

A safer and more effective treatment regimen for eclampsia

In a prospective controlled trial 91 consecutive women with eclampsia were randomly allocated either to a magnesium sulphate and nifedipine regime or to a lytic cocktail and nifedipine group. The type and severity of disease, details of labour and delivery, and the maternal and perinatal outcomes and complications related to the 2 treatment regimens were compared. Recurrence of fits, aspiration pneumonia and sudden hypotension were significantly reduced when patients were treated with the new magnesium sulphate and nifedipine regimen compared with the lytic cocktail plus nifedipine regimen. No patient treated with the new regimen died or had respiratory depression; in the other group there were 2 maternal deaths plus 1 case of severe hypoxic brain damage. No difference was observed in duration of labour or mode of delivery. Perinatal mortality was significantly lower in the magnesium sulphate plus nifedipine treated group. The synergistic action of magnesium sulphate and nifedipine in the dosage employed in this study may be used to reduce maternal and perinatal mortality and morbidity in women with eclampsia.

Magnesium sulfate potentiates several cardiovascular and metabolic actions of terbutaline

beta-Adrenergic agonists are useful for the emergency treatment of asthma. Recently, magnesium sulfate (MgSO4) has also been shown to be efficacious in this situation. beta-Agonists have unwanted cardiovascular and metabolic actions: increased systolic blood pressure, corrected QT interval (QTc), serum glucose and insulin, and decreased RR interval, diastolic blood pressure, serum potassium, phosphate, and calcium. As beta-agonists and MgSO4 quite possibly will be used in combination, we sought to determine how MgSO4 would affect these actions. Healthy young male adults were administered two doses of terbutaline sulfate, 0.25 mg subcutaneously, 30 min apart on two separate occasions, in a randomized, double-blind fashion. On one occasion, 4 g of MgSO4 was administered intravenously over the same 30-min period. On the other, normal saline solution was given as a placebo. Cardiovascular and metabolic variables were measured sequentially for 2 h. Data at 60 min with p values given for a summation of all time points are as follows: MgSO4 increased terbutaline's effects on the RR interval by 0.09 s, p < 0.0001; QTc interval by 0.01 s, p < 0.0007; diastolic blood pressure by 8 mm Hg, p = 0.0001; serum calcium by 0.13 mg/dl, p = 0.01; and glucose by 9 mg/dl, p < 0.0001. MgSO4 also mitigated the systolic blood pressure elevating the effect of terbutaline by 5 mm Hg (p = 0.007). The magnitude of the response potentiations was modest. We conclude that combining terbutaline and MgSO4 is unlikely to result in serious short-term adverse events, if used acutely in patients with relatively normal cardiac and metabolic function. MgSO4 may act by potentiating the effect of beta-agonists on magnesium requiring enzymes such as adenyl cyclase.

Acute tocolysis for fetal distress: terbutaline versus magnesium sulphate

Forty-six women in active labour who developed fetal distress requiring abdominal delivery were randomized to receive 0.25 mg of terbutaline (subcutaneously) or magnesium sulphate as a 4-g bolus (intravenously) to decrease uterine activity. The terbutaline-treated group in contrast to the magnesium sulphate-treated group had reduced uterine activity as measured by Montevideo units (p < 0.002). This decrease in uterine activity was noted more rapidly in all 23 patients who received terbutaline, 1.8 +/- 0.74 minutes compared to 7.5 +/- 2.1 minutes in the 16 of 23 patients (magnesium sulphate-treated women) in whom a decrease in uterine activity occurred (p < 0.001). Umbilical cord arterial blood pH at delivery was less than 7.20 in only 2 of the 23 patients treated with terbutaline versus 7 of the 23 in the magnesium sulphate-treated group. We conclude that terbutaline is an effective and more rapid-acting tocolytic agent to arrest uterine activity prior to delivery for fetal distress.

The efficacy of oral terbutaline after intravenous tocolysis

OBJECTIVE

Our purpose was to investigate in a prospective, randomized study the efficacy of oral terbutaline after successful intravenous tocolysis in reducing preterm birth.

STUDY DESIGN

Patients between 28 and 35 weeks' gestation with uterine contractions and change in cervical examination were treated with intravenous magnesium sulfate for 12 to 24 hours. After successful tocolysis patients were approached for study participation and randomized to receive either oral terbutaline or no therapy. The dose of terbutaline was individualized to achieve a maternal pulse > 100 beats/min, and terbutaline was continued until 36 completed weeks of gestation. Recurrent preterm labor (contractions with change in cervical examination) for either group was treated with intravenous magnesium sulfate, and subsequent treatment was based on the previous randomization.

RESULTS

Fifty-five patients were enrolled (28 terbutaline, 27 no oral tocolytic). No difference was found between groups with respect to time gained (4.0 +/- 2.7 vs 4.6 +/- 3.1 weeks, p = 0.412), gestational age at delivery (35.6 +/- 2.7 vs 36.1 +/- 2.4 weeks, p = 0.562), > or = 37 weeks at delivery (nine vs 13, p = 0.291), recurrent preterm labor (10 vs four, p = 0.104), recurrent uterine contractions alone (five vs eight, p = 0.527), birth weight (2616 +/- 633 gm vs 2645 +/- 599 gm, p = 0.785), special care nursery admissions (eight vs six, p = 0.759), or neonatal respiratory distress syndrome (three vs two, p = 0.965).

CONCLUSION

The use of oral terbutaline after successful parenteral tocolysis failed to reduce the rate of preterm birth.

Oral tocolysis with magnesium chloride: a randomized controlled prospective clinical trial

A prospective randomized clinical trial was conducted to assess the efficacy and safety of enteric-coated magnesium chloride (SLOW MAG) as an oral tocolytic agent. Seventy-five patients between 24 and 34 weeks' gestation who were treated with intravenous magnesium sulfate for a first episode of preterm labor were enrolled. After a 12-hour contraction-free period on intravenous therapy, patients were randomized by sealed envelope to one of three groups: group 1, SLOW MAG (535 mg every 4 hours); group 2, oral ritodrine (20 mg every 4 hours); or group 3, no therapy (control). Patients receiving oral therapy were treated until delivery or completion of 36 weeks' gestation. No difference was found between groups with respect to time gained with the use of oral therapy or number completing 36 weeks' gestation. Therapy with enteric-coated magnesium chloride was associated with significantly fewer side effects (20%) as compared with ritodrine (48%) (p less than 0.01). Our results suggest that compared with ritodrine, enteric-coated magnesium chloride is as effective in prolonging pregnancy and preventing recurrent preterm labor. However, neither enteric-coated magnesium chloride nor ritodrine appeared to be any more effective in the prevention of preterm delivery than observation alone.

Neuroophthalmologic effects of intravenous magnesium sulfate

To test the hypothesis that visual disturbances are more common during intravenous magnesium sulfate administration than at 1 to 4 days after discontinuation of the drug, 13 women underwent bedside neuroophthalmologic examinations during intravenous magnesium sulfate tocolysis at 2.0 to 3.0 gm hr and again at 1 to 4 days after cessation of therapy. Visual symptoms were common during intravenous magnesium sulfate administration. Blurred vision was present in 12 of 13 patients and diplopia was present in 10 of 13 patients. Abnormal findings during neuroophthalmologic examination occurred in all patients during intravenous magnesium sulfate administration. Findings included ptosis, accommodative and convergence insufficiency, and abnormal pupillary responsiveness to light and near. All patients were symptom-free and had normal examinations after magnesium sulfate was discontinued. These findings suggest that visual disturbances with therapeutic magnesium sulfate are common.

Effects of magnesium and isradipine on contractile activation induced by the thromboxane A2 analog U46619 in human uteroplacental arteries in term pregnancy

The effects of Mg++ and the dihydropyridine calcium channel blocker isradipine on contractions induced by the thromboxane A2 mimetic U46619 were studied in isolated human uteroplacental arteries. In all preparations investigated U46619 10(-10) to 10(-6) mol/L induced concentration-related contractile responses. In maternal vessels U46619 produced a biphasic concentration-response curve, whereas the compound in fetal vessels produced a sigmoid concentration-response curve parallel to that of prostaglandin F2 alpha. Mg++ (1.0 to 6.0 mmol/L) and isradipine (10(-10) to 10(-5) mol/L) both relaxed U46619-induced contractions by up to about 40%. In preparations precontracted by U46619 and exposed to isradipine 10(-6) mol/L, addition of Mg++ 6.0 mmol/L consistently produced a further small relaxation. Removal of the endothelium or pretreatment with indomethacin 10(-6) mol/L or digoxin 10(-6) mol/L did not influence the inhibition produced by Mg++ or isradipine. In vessels pretreated in Ca(++)-free medium Mg++ 6.0 mmol/L depressed and isradipine abolished responses to Ca++ (0.01 to 4.0 mmol/L) after depolarization with K+ 124 mmol/L. In maternal and fetal arteries stimulated with U46619, however, Mg++ 6.0 mmol/L and isradipine 10(-6) mol/L produced a similar, partial inhibition of responses to Ca++ (0.01 to 4.0 mmol/L). Mg++ seems to inhibit transmembrane Ca++ influx, although less efficiently than the dihydropyridine calcium antagonist isradipine. In addition, Mg++ may interfere with Ca++ at intracellular binding sites. Provided that preeclampsia comprises enhanced vascular actions of thromboxane A2, the present results support the established use of Mg++ in the treatment of this condition and suggest that calcium antagonists are of potential benefit.

Randomized investigation of magnesium sulfate for prevention of preterm birth

One hundred fifty-six women with preterm labor between 24 and 34 weeks' gestation were randomized to receive either intravenous magnesium sulfate or no tocolytic therapy. Magnesuim sulfate infusions of up to 3 gm/hr were used in 76 pregnancies and resulted in a mean serum magnesium concentration of 5.5 +/- 1.4 mEq/L (mean +/- SEM). Compared with 80 control pregnancies, magnesium sulfate tocolysis had no significant effect on duration of gestation, birth weight, neonatal morbidity, and perinatal mortality. We conclude that clinically safe infusions of magnesium sulfate are ineffective when used to prevent preterm birth.

Effects of magnesium on isolated human fetal and maternal uteroplacental vessels

The effects of Mg2+ were studied in human umbilical arteries, stem villous arteries and maternal intramyometrial arteries. The vessels were dissected and mounted in organ baths, and isometric tension was recorded. In all fetal preparations investigated, Mg2+ (0.5-6.0 mM) in a concentration-related way decreased pD2 values for prostaglandin F2 alpha responses. The maximum response to prostaglandin F2 alpha was depressed in umbilical arteries, but remained unaffected in stem villous artery preparations. In stem villous arteries pretreated in Ca2(+)-free medium, increasing concentrations of Mg2+ markedly depressed the response to Ca2+ after stimulation with K+ or prostaglandin F2 alpha, suggesting that Mg2+ inhibited transmembrane calcium influx and interfered with intracellular calcium effects. In both stem villous and intramyometrial arteries, increasing concentrations of Mg2+ increased EC50 values for responses to K+, whereas Emax values were unaffected. Mg2+ produced relaxation of agonist-induced contractions by up to 60% in stem villous arteries and up to 40% in intramyometrial artery preparations. The relaxant effect of Mg2+ did not seem to be mediated through the endothelium or through changes in the synthesis of prostanoids, since endothelial disruption and treatment with indomethacin left the responses to Mg2+ unaffected. Relaxation of vessels important for resistance regulation in the human uteroplacental vascular bed may be of benefit when uteroplacental blood flow is impaired, and the present results support the established use of magnesium sulphate in the treatment of pre-eclampsia.

Prospective study on premature labor with magnesium sulfate

The efficacy of magnesium sulfate was evaluated as the primary tocolytic agent in the management of patients at risk for premature delivery. Fifteen patients presenting with premature labor between 28 and 35 weeks gestation, given titrated dose intravenously magnesium sulfate till uterine contraction ceased, were prospectively studied. All patients received an additional oral beta-mimetic agent once labor was arrested till 36 weeks gestation. All cases had intact membranes and no contraindications for tocolytic therapy. Tocolysis for more than 72 hours was achieved in 14 cases (93.3%). Delayed tocolysis of more than 7 days was achieved in 13 cases (86.7%). The mean dosage to achieve tocolytic effect was 3.17 g/hr (SD 0.08). The mean serum magnesium level to achieve such effect was 5.38 mg/dl (SD 0.88). Magnesium sulfate was found to be easy to administer and clinically efficacious with minimal adverse effects. It may be used as the first line of tocolytic therapy where beta-sympathomimetic drugs are contraindicated.

Magnesium tocolysis: serum levels versus success

The relationship between maternal serum magnesium levels and tocolytic success is poorly established. We performed a retrospective analysis of 101 episodes of preterm labor treated with magnesium sulfate and compared the initial, average, and maximum serum magnesium levels with tocolytic success at 48 hours and 7 days. There was no difference in the proportions of tocolytic success when serum levels were less than 6 mg/dl compared with levels of greater than or equal to 6 mg/dl. Similar analyses on either side of 5 mg/dl also revealed no significant relationship. Mean serum magnesium levels in patients with successful tocolysis were statistically similar to those of patients in whom tocolysis failed. Multiple logistic regression analysis also failed to establish a positive relationship between serum magnesium levels and tocolytic success. We conclude that serum magnesium levels alone should not serve as an end point of therapy.

Congenital rickets associated with magnesium sulfate infusion for tocolysis

The records of five neonates born to mothers treated with intravenously administered magnesium sulfate for tocolysis were retrospectively reviewed to assess the presence of radiographic, clinical, and biochemical abnormalities. Two infants had radiographic bony abnormalities; one had frank rachitic changes and dental enamel hypoplasia. One of these patients, as well as an additional infant, had transient hypocalcemia. We hypothesize that prolonged infusion of magnesium sulfate, especially when initiated during the second trimester, may lead to fetal parathyroid gland suppression with consequent abnormalities resembling rickets.

Efficacy and side effects of magnesium sulfate and ritodrine as tocolytic agents

Ritodrine as the first-line drug in the treatment of established preterm labor has been supplanted in some centers by magnesium sulfate. To assess the relative efficacy and rates of side effects of these two agents, 120 patients were randomly assigned to receive one of these two drugs. Patients were included if they had intact membranes and met strict criteria for the definition of labor. In both groups excellent outcome was achieved, with 96.3% and 92.3% of patients receiving ritodrine and magnesium sulfate, respectively, obtaining a delay in delivery of greater than 48 hours. Side effects were comparable in both groups, although they tended to be more serious in the patients receiving ritodrine. In patients receiving both drugs together, the rate of side effects was 77% without a demonstrable benefit over a single agent. We conclude that ritodrine and magnesium sulfate are tocolytics of comparable efficacy and when used aggressively are highly successful in delaying delivery.

Early versus late tocolytic treatment for preterm premature membrane rupture

The effect of tocolytic therapy before labor was evaluated in 33 pregnant women with preterm premature rupture of the membranes. Either intravenous magnesium sulfate or oral terbutaline was administered at the time of presentation. Intensive surveillance to detect signs of infection was carried out for all patients. In 29 of the patients in this treatment group who were seen at less than 34 weeks, a significantly longer prolongation of pregnancy was achieved when compared with 24 similar women treated after onset of labor in the hospital (169 hours versus 77 hours, p = 0.05). Duration of infant hospitalization was less for those mothers receiving tocolytic agents before labor. Maternal and infant infection were not different in the two groups; nor was the cesarean section rate. When this treatment group was compared with another control group of 96 women already in labor at presentation, the difference in time from admission to delivery was substantial, but it did not achieve statistical significance. In this group the rate of maternal infection was significantly higher, but newborn morbidity was not. Aggressive early treatment with tocolytic agents in pregnant women with preterm premature membrane rupture is more productive but not more dangerous than conservative management.

Myocardial contractility and performance capacity after magnesium infusions in young healthy persons: a double-blind, placebo-controlled, cross-over study

To evaluate the effect of intravenous magnesium (Mg) treatment on the inotropic state of the heart and maximal work capacity, 9 healthy volunteers were entered in a double-blind, placebo-controlled, cross-over study. Separated by an interval of three weeks, the volunteers were tested twice, each time randomly allocated to receive either an intravenous injection of 10 mmol magnesium chloride dissolved in 100 ml isotonic sodium chloride or placebo of isotonic sodium chloride only. Before and after each infusion myocardial inotropism was evaluated by echocardiography. Mitral-septal distance (MSA) was used as a measure for ejection fraction. On each test day an ergometer bicycle exercise test was performed, and maximal work capacity was calculated. Magnesium treatment reduced the MSA (from 4.2 to 2.9 mm, p = 0.07), while no difference was found after placebo treatment. Likewise, a tendency toward increasing fractional shortening after magnesium treatment was detected, although this difference was not statistically significant (p = 0.1). No difference in maximal work capacity between the magnesium and placebo periods was found. Serum magnesium concentrations and placebo periods was found. Serum magnesium concentrations rose significantly after the infusions (from 0.82 to 1.38 mmol/l, p less than 0.001). It is concluded that intravenous magnesium does not exert a negative inotropic effect on the myocardium as previously stated. On the contrary, we found a tendency toward a positive inotropic effect. However, the observed differences are of borderline statistical significance and a more extended study, employing invasive measurements of cardiac inotropism appears to be necessary.

Comparison of oral ritodrine and magnesium gluconate for ambulatory tocolysis

Magnesium sulfate has been administered intravenously to arrest preterm labor but the oral form of this drug cannot be used for continual tocolysis. This trial involved the administration of oral magnesium gluconate to determine its effectiveness compared with that of ritodrine hydrochloride in 50 patients whose labor had been arrested by parenteral therapy. Group A (n = 25) received 1 gm of oral magnesium gluconate every 2 to 4 hours for tocolysis and group B (n = 25) received 10 mg of ritodrine every 2 to 4 hours. The number of patients who progressed to 37 weeks' gestation was similar (group A, 21 versus group B, 19) and the time gained in utero was not different (group A, 6.4 weeks versus group B, 5.9 weeks). There was a trend toward more side effects with the use of ritodrine (40%) compared with magnesium gluconate (16%), but the numbers were too small to reveal a significant difference. These data suggest that magnesium gluconate used as an oral tocolytic is as effective as a beta-agonist in patients whose labor is arrested initially with intravenous therapy.

Magnesium sulfate and ritodrine hydrochloride: a randomized comparison

The efficacy of magnesium sulfate was analyzed in relation to ritodrine hydrochloride. Patients presenting in preterm labor between 20 and 35 weeks' gestation were prospectively randomized. Tocolysis was achieved for more than 72 hours in 35 of 40 cases (88%) where magnesium sulfate was administered and 31 of 39 cases (79%) in which ritodrine hydrochloride was infused. Delay of greater than or equal to 7 days was achieved in 75% and 72% of cases, respectively. The mean dosage to achieve tocolysis was 4.5 gm/hr, in the magnesium sulfate group and 210.0 micrograms/hr in ritodrine hydrochloride-treated patients. The mean magnesium level to achieve tocolysis was 6.60 mg/dl. Side effects in the two groups were similar in number but less alarming in the magnesium sulfate group. Magnesium sulfate was found to be easy to administer and clinically efficacious. Its tocolytic action was found to be dose dependent and drug concentrations are easily determined. On the basis of this work and data from other investigators, magnesium sulfate should be used as the first line of tocolytic therapy with ritodrine hydrochloride as its pharmacologic backup.

A comparison of ritodrine, terbutaline, and magnesium sulfate for the suppression of preterm labor

Ritodrine, terbutaline, and magnesium sulfate have all been used in the United States as tocolytic drugs. Studies have shown each of these drugs to be effective in suppressing preterm labor. The current study was undertaken in order to compare their relative safety and efficacy and to evaluate the effectiveness of a second drug when the first-used drug failed to stop contractions. No differences in efficacy could be demonstrated between the drugs; however, there was a marked difference in the incidence of maternal side effects. Because of an unacceptable level of side effects, we have stopped the use of terbutaline at our institution.

Magnesium sulfate and ritodrine hydrochloride: systemic and uterine hemodynamic effects

Effects of magnesium sulfate and ritodrine hydrochloride on cardiovascular physiologic characteristics were studied in 70 human subjects treated for preterm labor. Systemic and uterine hemodynamic effects were investigated in five pregnant rhesus monkeys. Systolic blood pressure was minimally affected by either agent. Diastolic pressure, while not affected by magnesium sulfate, decreased 26.3% during ritodrine therapy. Maternal and fetal heart rates were minimally affected by magnesium sulfate. Ritodrine increased maternal and fetal heart rates significantly. In the monkeys, magnesium sulfate increased uterine and placental blood flows (by the microsphere technique) but failed to alter cardiac output. Ritodrine produced an increase in cardiac output but decreased perfusion pressure. Placental blood flow decreased by an average of 27.6%. Ritodrine would therefore seem contraindicated with a compromised fetal environment. Magnesium sulfate, by not altering perfusion pressure, may have a beneficial effect on uterine hemodynamics. These specific and distinct differences in cardiovascular and hemodynamic effects should be considered when either magnesium sulfate or ritodrine is selected as a tocolytic agent.

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.

Addition of magnesium sulfate improves effectiveness of ritodrine in preventing premature delivery

From October, 1981, to July, 1983, 225 patients were evaluated for premature labor at Forsyth Memorial Hospital. Sixty-five of these patients were considered to be candidates for intravenous ritodrine treatment. Of this group, 24 patients were successfully treated and had pregnancy prolongation ranging from 1 to 17 weeks. Forty-one patients did not respond to maximal intravenous ritodrine therapy (300 to 350 micrograms/min). Eleven patients subsequently delivered within 24 to 48 hours of treatment initiation. The remaining 30 patients received intravenous magnesium sulfate (1 to 3 gm/hr) in addition to intravenous ritodrine. Eighteen patients responded favorably to this combination treatment and had pregnancy prolongation ranging from 1 to 11 weeks. Twelve patients delivered within 1 week from treatment initiation. In all cases where pregnancy prolongation was achieved, birth weight and neonatal outcome were significantly improved compared to patients who did not respond to either intravenous ritodrine alone or intravenous ritodrine and magnesium sulfate combination. Treatment related maternal/fetal complications were not significantly different in the various groups examined. From the foregoing we conclude that, in a select group of patients in premature labor not responding to conventional ritodrine therapy, magnesium supplementation in pharmacologic doses could have a beneficial effect with respect to pregnancy outcome.

Prevention of preterm delivery. The important role of early recognition

Perinatal deaths can be decreased most effectively by reducing the incidence of preterm delivery. Therapy with a tocolytic agent, such as ritodrine ( Yutopar ), can be of significant benefit if applied to patients in whom preterm labor is correctly diagnosed and has not advanced beyond the early stages. Identification of the patient at risk, intensive education and surveillance of such patients, and education of hospital and clinic staff can extend the application and success of labor-inhibiting therapy.

The influence of hypermagnesemia on serum calcium and parathyroid hormone levels in human subjects

We measured serum concentrations of calcium and parathyroid hormone in seven pregnant women who were receiving intravenous magnesium sulfate for the suppression of premature labor. After administration of magnesium sulfate, the mean (+/- S.E.M.) serum magnesium level rose rapidly from the normal base-line level of 2.0 +/- 0.2 mg per deciliter to 6.1 +/- 0.4 mg per deciliter (0.8 +/- 0.1 to 2.5 +/- 0.2 mmol per liter) (P less than 0.001) at 30 minutes and remained markedly elevated. Concentrations of total and ionized calcium fell gradually in all subjects from normal base-line concentrations, 8.6 +/- 0.2 and 4.4 +/- 0.1 mg per deciliter (2.2 +/- 0.1 and 1.1 +/- 0.03 mmol per liter), respectively, into the hypocalcemic range, reaching a nadir of 7.6 +/- 0.2 and 3.9 +/- 0.1 mg per deciliter (1.9 +/- 0.1 and 0.98 +/- 0.03 mmol per liter), respectively, at three hours (P less than 0.001). Parathyroid hormone levels fell rapidly in response to magnesium infusion, from 13.1 +/- 2.5 to 7.8 +/- 0.7 pg per milliliter at 30 minutes, and were significantly below base-line levels for two hours despite frank hypocalcemia. These results suggest that hypermagnesemia rapidly decreases the secretion of parathyroid hormone in vivo in human subjects and that parathyroid hormone levels remain depressed despite concomitant hypocalcemia. The results also suggest that the hypocalcemia associated with hypermagnesemia may be due in part to the suppressive effects of hypermagnesemia on parathyroid hormone secretion.

Adjunctive use of magnesium sulfate with ritodrine for preterm labor tocolysis

The purpose of the study was to determine if the adjunctive administration of magnesium sulfate with ritodrine would result in decreased dosage requirements of ritodrine, and, therefore, decrease the incidence of ritodrine-associated side effects. Candidates for tocolysis were prospectively randomized so that some received a uniform tocolytic dose of magnesium sulfate in a blinded protocol. All patients received a ritodrine infusion which was titrated in the standard manner to achieve cessation of labor. Evaluations included interval cumulative ritodrine dose, maximal ritodrine infusion rate, fluid balance, and blood chemistry studies. Contrary to our hypothesis, there were significantly more cardiovascular effects in the group that received ritodrine plus magnesium sulfate (11/24) than in the group that received ritodrine alone (1/17) (p less than or equal to 0.02). The predominant side effect was chest pain, frequently associated with electrocardiogram changes indicative of myocardial ischemia. These results are consistent with the current understanding of the regulatory mechanisms of these tocolytic agents. We conclude from the results of our prospective, randomized, blinded study that the adjunctive use of magnesium sulfate with ritodrine is associated with an unacceptable increase in serious side effects and probably does not improve efficacy.

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.