Calcium channel blockers for tocolysis: A review of their role and safety following reports of serious adverse events

A Detailed Review of Critical Care Considerations for the Pregnant Cardiac Patient

Maternal cardiovascular disease is a leading cause of maternal death worldwide and recently, maternal mortality has increased secondary to cardiovascular causes. Maternal admissions to critical care encompass 1%-2% of all critical care admissions, and although not common, the management of the critically ill pregnant patient is complex. Caring for the critically ill pregnant cardiac patient requires integration of pregnancy-associated physiologic changes, understanding pathophysiologic disease states unique to pregnancy, and a multidisciplinary approach to timing around delivery as well as antenatal and postpartum care. Herein we describe cardiorespiratory changes that occur during pregnancy and the differential diagnosis for cardiorespiratory failure in pregnancy. Cardiorespiratory diseases that are either associated or exacerbated by pregnancy are highlighted with emphasis on perturbations secondary to pregnancy and appropriate management strategies. Finally, we describe general management of the pregnant cardiac patient admitted to critical care.

Effects of nifedipine on fetal cardiac function in preterm labor

Objectives To evaluate the effects of nifedipine treatment on fetal hemodynamics and cardiac function during preterm labor. This prospective study assessed several quantitative parameters of fetal cardiac circulation and function, and found no significant changes at 48 h after nifedipine treatment. These findings suggest that tocolytic nifedipine may be safe for fetuses. It supports clinicians to use nifedipine treatment for tocolysis without any cardiac effect on the fetus. Methods A prospective cohort study was conducted at a tertiary hospital between January 2016 and October 2017. A total of 45 pregnant women who required nifedipine for preterm labor were included in this study. Fetal Doppler ultrasound was performed and fetal systolic and diastolic function was measured prior to, and 48 h after, the first nifedipine treatment. Conventional Doppler parameters were used to evaluate fetal heart function and hemodynamic changes. Tricuspid annular plane systolic excursion, mitral annular plane systolic excursion and the sphericity index were also evaluated to assess changes in fetal cardiac morphology. Results No significant changes in fetal Doppler parameters were observed following nifedipine tocolysis. There was no significant difference in the fetal cardiac function parameters of both ventricles before vs. after nifedipine treatment. Tricuspid annular plane systolic excursion, mitral annular plane systolic excursion, and sphericity index values were unchanged following nifedipine treatment. Conclusions Oral administration of nifedipine did not to alter fetal cardiac function or morphology. Fetal cardiac parameters and various Doppler indices were unchanged following nifedipine treatment. Maternal nifedipine treatment does not appear to have any significant effect on fetal cardiac function.

Does nifedipine improve outcomes of embryo transfer?: Interim analysis of a randomized, double blinded, placebo-controlled trial

BACKGROUND

Implantation failure is the main factor affecting the success rate of in vitro fertilization (IVF) procedures. Studies have reported that uterine contractions (UC) at the time of embryo transfer (ET) were inversely related to implantation and pregnancy rate, hence reducing the success of IVF treatments. Various pharmacological agents, with the exception of calcium channel blockers, have been investigated to improve ET outcomes by reducing UC. Thus, a double-blinded randomized, placebo-controlled trial was conducted to determine whether nifedipine, a calcium channel blocker with potent smooth muscle relaxing activity and an excellent safety profile, can improve the outcome of patients undergoing ET treatments.

METHODS

Ninety-three infertile women were recruited into 1 of 2 groups: placebo (n = 47) or nifedipine 20 mg (n = 46). Study participants were admitted 30 minutes prior to ET and given either tablet after their baseline vital signs were recorded. They then underwent ET and were observed for adverse events for another 30 minutes post-ET. Follow up of the participants' outcomes was conducted via electronic medical records. The primary outcomes are implantation and clinical pregnancy rates. Secondary outcomes include any maternal or fetal adverse events, miscarriage, pregnancy, live births, and neonatal outcomes. Resulting data were then analyzed using t test, Pearson chi-square test, and Fisher exact test to compare outcomes between the 2 groups.

RESULTS

No statistical differences in the implantation rate (42.6% vs 39.1%, P = .737, rate ratio 0.868, 95% confidence interval [CI]: 0.379-1.986) and the clinical pregnancy rate (23.4% vs 26.1%, P = .764, rate ratio 1.155, 95% CI: 0.450-2.966) were detected between the placebo and the treatment groups. In addition, no statistical significance between the placebo and the treatment groups for any secondary outcomes were detected.

CONCLUSIONS

This double blinded, randomized, and placebo-controlled trial demonstrated that the single use of 20 mg nifedipine given 30 minutes before embryo transfer did not improve the implantation rate or the clinical pregnancy rate of the infertility treatment. Further studies are required to demonstrate the clinical benefits and risks of nifedipine usage in embryo transfer.

Acute Tocolysis - a Critical Analysis of Evidence-Based Data

Tocolysis is among the most common obstetric measures. The objective is to prolong the pregnancy by at least 48 hours to complete foetal lung maturation and for the in-utero transfer of the pregnant woman to a perinatal centre. The indication for tocolysis is regular, premature contractions (≥ 4/20 min) and a dynamic shortening of the cervical length/cervical opening between 22 + 0 to 33 + 6 weeks of pregnancy. In this connection, the cervical length measured on ultrasound and the determination of biomarkers in the cervicovaginal secretions can be important decision-making aids. Beta sympathomimetics should no longer be used due to the high rate of severe maternal adverse effects. Given controversial data, magnesium sulphate is no longer recommended for tocolysis in current guidelines. Atosiban is as effective for prolonging pregnancy as beta sympathomimetics and nifedipine, has the lowest rate of maternal adverse effects, but also the highest drug costs. Nifedipine and indomethacin are recommended in international guidelines for acute tocolysis, however there are indications of increased neonatal morbidity following indomethacin. Current problems are, above all, the lack of randomised, controlled comparative and placebo-controlled studies, the data which are controversial to some extent, and the insufficient evidence of tocolytics to significantly improve the neonatal outcome.

[Adverse effects and hemodynamic effects of nifedipine as a tocolytic]

OBJECTIVES

To describe maternal and fetal adverse effects, in particular cardiorespiratory, of nifedipine as tocolytic, as well as effects on hemodynamic parameters.

MATERIALS AND METHODS

A retrospective evaluative study describing the use of nifedipine as tocolytic at CHU Sainte-Justine in Montreal. Demographic data as well as maternal blood pressure and adverse effects, and maternal and fetal heart rate were collected from medical records of women treated with nifedipine following our tocolysis protocol between January 1st 2004 and March 1st 2007.

RESULTS

The medical records of 213 pregnant women were included in the study. Cardiorespiratory adverse effects were noted in 69 (32.4%); of these, 19 (8.9%) had serious cardiorespiratory adverse events, including 6 acute pulmonary edema or overload. Mean maternal systolic and diastolic blood pressures were significantly decreased and mean maternal and fetal heart rates were significantly increased after the bolus dose. Other adverse effects were reported for 100 (46.9%) women.

CONCLUSION

Nifedipine may cause cardiorespiratory adverse effects warranting a close monitoring.

Maternal and fetal haemodynamic effects of nifedipine in normotensive pregnant women

While nifedipine is commonly used for tocolysis, the controversy on its safety remains. So far, the haemodynamic effects on maternal and fetal circulations have not been well documented. Fifteen normotensive women who received 20 mg nifedipine were included in this prospective observational study. The maternal and fetal haemodynamic effects were analysed using maternal echocardiography and fetal Doppler ultrasonography. Nifedipine induced a significant afterload reduction in all women. It triggered a compensatory increase in cardiac output, which maintained blood pressure. These maternal changes had no influence on the uteroplacental and fetal circulations.

ATP-sensitive potassium channels modulate in vitro tocolytic effects of β₂-adrenergic receptor agonists on uterine muscle rings in rats in early but not in late pregnancy

Aim

To investigate whether ATP-sensitive potassium (K_ATP) channels modulate the tocolytic effect of β₂-AR agonists (ritodrine and salmeterol) in early-pregnant (day 6) and late-pregnant (day 22) rat uterus in vitro, in order to examine the relation between the K_ATP channel sulphonylurea-binding regulatory subunit (SUR) expression and pharmacological reactivity of β₂-AR agonists.

Methods

The tocolytic effects of ritodrine and salmeterol (10^-10-10^-5 M) on spontaneous rhythmic contractions were investigated cumulatively, alone, or in the presence of the K_ATP channel blocker glibenclamide (10^-6 M) and the K_ATP channel opener pinacidil (10^-9-10^-7 M) after 5-min preincubation.

Results

β₂-AR agonist induced myometrial relaxation was inhibited by glibenclamide and enhanced by pinacidil on day 6, when SUR1 expression levels were high. Neither glibenclamide nor pinacidil mediated tocolytic effect was measured on day 22.

Conclusion

Low expression of the K_ATP channels at the end of gestation may facilitate enhanced excitability and contractility in the rat myometrium. The combination of a betamimetic and a K_ATP channel opener will therefore not be of therapeutic relevance in the treatment of preterm delivery.

Off-label use of nicardipine as tocolytic and acute pulmonary oedema: a post-marketing analysis of adverse drug reaction reports in EudraVigilance

PURPOSE

To evaluate a signal of acute pulmonary oedema (APO) due to nicardipine used off-label as tocolytic in pregnant women.

METHODS

All the suspected cases of APO recorded in EudraVigilance database up to 31/01/2013 and associated with nicardipine containing medicinal products were retrieved. The Proportional Reporting Ratio was considered as measure of disproportionality. Individual cases evaluation was conducted.

RESULTS

Thirty-four spontaneous cases regarding pregnancy women who experienced APO following nicardipine treatment as tocolytic were collected. The detected proportional reporting ratio was 50.96 (95% confidence interval lower bound equal to 36.75). The analysis focused on 10 serious cases. Most women, aged between 27 and 39 years, were treated with intravenous nicardipine. The most of the suspected adverse reactions occurred between 24 and 96 hours.

CONCLUSIONS

A potentially causal association between APO and off-label use of nicardipine as tocolytic has been detected during a periodic signal detection activity. The Pharmacovigilance Risk Assessment Committee confirmed our findings, recommending an update of the summary of the product characteristics for medicines containing nicardipine for both intravenous and oral formulations. Then European Medicines Agency reaffirmed that nicardipine use in other indications is no longer recommended.

Hemodynamic effects of nifedipine tocolysis

AIM

To describe the effects of nifedipine tocolysis on blood pressure and heart rate in non-hypertensive women.

METHODS

This was a retrospective study from 2001 to 2011 to compare blood pressures and heart rates among non-hypertensive women on nifedipine tocolysis up to 8 h after nifedipine initiation. Measurements at 20-60 and 61-120 min were compared to assess the differential effects of dosing on hemodynamics and reflected the effects of the initial and complete loading doses, respectively. Charts were reviewed for hypotension-related emergent delivery.

RESULTS

One hundred and thirty-eight patients were included. Over the 8-h study interval, mean systolic blood pressure (P < 0.001) and mean diastolic blood pressure (P < 0.001) decreased by 5 mmHg and heart rate increased by 4 b.p.m. (P < 0.001). Systolic and diastolic blood pressures were unchanged from baseline up to 120 min at all doses. Heart rate increased at both 20-60 and 61-120 min when all doses were considered (P < 0.001), but differential dosing effects were not observed. Rates of tachycardia increased (P < 0.001), but rates of hypotension were unchanged. No hypotension-related emergent deliveries occurred.

CONCLUSION

Nifedipine tocolysis was associated with hemodynamic changes in non-hypertensive women. Tachycardia was increased but hypotension was unaffected, supporting the general safety of nifedipine in this setting.

Nicardipine-induced acute pulmonary edema: a rare but severe complication of tocolysis

We report four cases of acute pulmonary edema that occurred during treatment by intravenous tocolysis using nicardipine in pregnancy patients with no previous heart problems. Clinical severity justified hospitalization in intensive care unit (ICU) each time. Acute dyspnea has begun at an average of 63 hours after initiation of treatment. For all patients, the first diagnosis suspected was pulmonary embolism. The patients' condition improved rapidly with appropriate diuretic treatment and by modifying the tocolysis. The use of intravenous nicardipine is widely used for tocolysis in France even if its prescription does not have a marketing authorization. The pathophysiological mechanisms of this complication remain unclear. The main reported risk factors are spontaneous preterm labor, multiple pregnancy, concomitant obstetrical disease, association with beta-agonists, and fetal lung maturation corticotherapy. A better knowledge of this rare but serious adverse event should improve the management of patients. Nifedipine or atosiban, the efficiency of which tocolysis was also studied, could be an alternative.

The effect of trichostatin-A and tumor necrosis factor on expression of splice variants of the MaxiK and L-type channels in human myometrium

The onset of human parturition is associated with up-regulation of pro-inflammatory cytokines including tumor necrosis factor (TNF) as well as changes in ion flux, principally Ca²⁺ and K⁺, across the myometrial myocytes membrane. Elevation of intra-cellular Ca²⁺ from the sarcoplasmic reticulum opens L-type Ca²⁺ channels (LTCCs); in turn this increased calcium level activates MaxiK channels leading to relaxation. While the nature of how this cross-talk is governed remains unclear, our previous work demonstrated that the pro-inflammatory cytokine, TNF, and the histone deacetylase inhibitor, Trichostatin-A (TSA), exerted opposing effects on the expression of the pro-quiescent Gαs gene in human myometrial cells. Consequently, in this study we demonstrate that the different channel splice variants for both MaxiK and LTCC are expressed in primary myometrial myocytes. MaxiK mRNA expression was sensitive to TSA stimulation, this causing repression of the M1, M3, and M4 splice variants. A small but not statistically significantly increase in MaxiK expression was also seen in response to TNF. In contrast to this, expression of LTCC splice variants was seen to be influenced by both TNF and TSA. TNF induced overall increase in total LTCC expression while TSA stimulated a dual effect: causing induction of LTCC exon 8 expression but repressing expression of other LTCC splice variants including that encoding exons 30, 31, 33, and 34, exons 30–34 and exons 40–43. The significance of these observations is discussed herein.

Calcium channel blockers for inhibiting preterm labour and birth

BACKGROUND

Preterm birth is a major contributor to perinatal mortality and morbidity, affecting around 9% of births in high-income countries and an estimated 13% of births in low- and middle-income countries. Tocolytics are drugs used to suppress uterine contractions for women in preterm labour. The most widely used tocolytic are the betamimetics, however, these are associated with a high frequency of unpleasant and sometimes severe maternal side effects. Calcium channel blockers (CCBs) (such as nifedipine) may have similar tocolytic efficacy with less side effects than betamimetics. Oxytocin receptor antagonists (ORAs) (e.g. atosiban) also have a low side-effect profile.

OBJECTIVES

To assess the effects on maternal, fetal and neonatal outcomes of CCBs, administered as a tocolytic agent, to women in preterm labour.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (12 November 2013).

SELECTION CRITERIA

All published and unpublished randomised trials in which CCBs were used for tocolysis for women in labour between 20 and 36 completed weeks' gestation.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial eligibility, undertook quality assessment and data extraction. Results are presented using risk ratio (RR) for categorical data and mean difference (MD) for data measured on a continuous scale with the 95% confidence interval (CI). The number needed to treat to benefit (NNTB) and the number needed to treat to harm (NNTH) were calculated for categorical outcomes that were statistically significantly different.

MAIN RESULTS

This update includes 26 additional trials involving 2511 women, giving a total of 38 included trials (3550 women). Thirty-five trials used nifedipine as the CCB and three trials used nicardipine. Blinding of intervention and outcome assessment was undertaken in only one of the trials (a placebo controlled trial). However, objective outcomes defined according to timing of birth and perinatal mortality were considered to have low risk of detection bias.Two small trials comparing CCBs with placebo or no treatment showed a significant reduction in birth less than 48 hours after trial entry (RR 0.30, 95% CI 0.21 to 0.43) and an increase in maternal adverse effects (RR 49.89, 95% CI 3.13 to 795.02, one trial of 89 women). Due to substantial heterogeneity, outcome data for preterm birth (less than 37 weeks) were not combined; one placebo controlled trial showed no difference (RR 0.96, 95% CI 0.89 to 1.03) while the other (non-placebo controlled trial) reported a reduction (RR 0.44, 95% CI 0.31 to 0.62). No other outcomes were reported.Comparing CCBs (mainly nifedipine) with other tocolytics by type (including betamimetics, glyceryl trinitrate (GTN) patch, non-steriodal anti inflammatories (NSAID), magnesium sulphate and ORAs), no significant reductions were shown in primary outcome measures of birth within 48 hours of treatment or perinatal mortality.Comparing CCBs with betamimetics, there were fewer maternal adverse effects (average RR 0.36, 95% CI 0.24 to 0.53) and fewer maternal adverse effects requiring discontinuation of therapy (average RR 0.22, 95% CI 0.10 to 0.48). Calcium channel blockers resulted in an increase in the interval between trial entry and birth (average MD 4.38 days, 95% CI 0.25 to 8.52) and gestational age (MD 0.71 weeks, 95% CI 0.34 to 1.09), while decreasing preterm and very preterm birth (RR 0.89, 95% CI 0.80 to 0.98 and RR 0.78, 95% CI 0.66 to 0.93); respiratory distress syndrome (RR 0.64, 95% CI 0.48 to 0.86); necrotising enterocolitis (RR 0.21, 95% CI 0.05 to 0.96); intraventricular haemorrhage (RR 0.53, 95% CI 0.34 to 0.84); neonatal jaundice (RR 0.72, 95% CI 0.57 to 0.92); and admissions to neonatal intensive care unit (NICU) (average RR 0.74, 95% CI 0.63 to 0.87). No difference was shown in one trial of outcomes at nine to twelve years of age.Comparing CCBs with ORA, data from one study (which did blind the intervention) showed an increase in gestational age at birth (MD 1.20 completed weeks, 95% CI 0.25 to 2.15) and reductions in preterm birth (RR 0.64, 95% CI 0.47 to 0.89); admissions to the NICU (RR 0.59, 95% CI 0.41 to 0.85); and duration of stay in the NICU (MD -5.40 days,95% CI -10.84 to 0.04). Maternal adverse effects were increased in the CCB group (average RR 2.61, 95% CI 1.43 to 4.74).Comparing CCBs with magnesium sulphate, maternal adverse effects were reduced (average RR 0.52, 95% CI 0.40 to 0.68), as was duration of stay in the NICU (days) (MD -4.55, 95% CI -8.17 to -0.92). No differences were shown in the comparisons with GTN patch or NSAID, although numbers were small.No differences in outcomes were shown in trials comparing nicardipine with other tocolytics, although with limited data no strong conclusions can be drawn. No differences were evident in a small trial that compared higher- versus lower-dose nifedipine, though findings tended to favour a high dose on some measures of neonatal morbidity.

AUTHORS' CONCLUSIONS

Calcium channel blockers (mainly nifedipine) for women in preterm labour have benefits over placebo or no treatment in terms of postponement of birth thus, theoretically, allowing time for administration of antenatal corticosteroids and transfer to higher level care. Calcium channel blockers were shown to have benefits over betamimetics with respect to prolongation of pregnancy, serious neonatal morbidity, and maternal adverse effects. Calcium channel blockers may also have some benefits over ORAs and magnesium sulphate, although ORAs results in fewer maternal adverse effects. However, it must be noted that no difference was shown in perinatal mortality, and data on longer-term outcomes were limited. Further, the lack of blinding of the intervention diminishes the strength of this body of evidence. Further well-designed tocolytic trials are required to determine short- and longer-term infant benefit of CCBs over placebo or no treatment and other tocolytics, particularly ORAs. Another important focus for future trials is identifying optimal dosage regimens of different types of CCBs (high versus low, particularly addressing speed of onset of uterine quiescence) and formulation (capsules versus tablets). All future trials on tocolytics for women in preterm labour should employ blinding of the intervention and outcome assessment, include measurement of longer-term effects into early childhood, and also costs.

Calcium channel blockers as tocolytics: principles of their actions, adverse effects and therapeutic combinations

Dihydropyridine Ca²⁺ channel blockers (CCBs) are widely accepted in the treatment of premature labour. Their mechanism of action in tocolysis involves the blockade of L-type Ca²⁺ channels, influenced by the Ca²⁺-activated K⁺ channels, beta-adrenergic receptors (β-ARs) and sexual hormones. In clinical practice, most experience has been gained with the use of nifedipine, whose efficacy is superior or comparable to those of β-agonists and oxytocin antagonists. Additionally, it has a favourable adverse effect profile as compared with the majority of other tocolytics. The most frequent and well-tolerated side-effects of CCBs are tachycardia, headache and hypotension. In tocolytic therapy efforts are currently being made to find combinations of tocolytic agents that yield better therapeutic action. The available human and animal studies suggest that the combination of CCBs with β-AR agonists is beneficial, although such combinations can pose risk of pulmonary oedema in multiple pregnancies and maternal cardiovascular diseases. Preclinical data indicate the potential benefit of combinations of CCBs and oxytocin antagonists. However, the combinations of CCBs with progesterone or cyclooxygenase inhibitors may decrease their efficacy. The CCBs are likely to remain one of the most important groups of drugs for the rapid inhibition of premature uterine contractions. Their significance may be magnified by further clinical studies on their combined use for tocolysis.

Antenatal calcium channel blocker exposure and subsequent patent ductus arteriosus in extremely low-birth-weight infants

This study aimed to assess whether tocolytic fetal exposure to antenatal calcium channel blockers (aCCB) increases the risk for hemodynamically significant patent ductus arteriosus (hsPDA) in extremely low-birth-weight (ELBW) infants. This case-control study investigated ELBW infants (<1,000 g) without cardiac defects in a level 3 neonatal intensive care unit who had survived at least 7 days. Nifedipine was the only aCCB used for this study population. The measurements included the history of aCCB exposure, selected maternal data, hsPDA diagnosis, gestational age at birth, birth weight, mode of delivery, sex, maternal race, location of birth, Apgar scores, and selected neonatal morbidities. The end point of the study was hsPDA, defined as an echocardiographically confirmed PDA with clinical symptoms. A total of 180 infants met the study criteria. The diagnosis was hsPDA for 56% of these patients, 20% of whom had aCCB exposure. Of the infants without hsPDA, 11% had aCCB exposure (p = 0.09). No statistically significant associations were found between aCCB exposure and hsPDA after adjustment for gestational age (odds ratio [OR], 1.5; 95% confidence interval [CI], 0.6-3.7) or for gestational age and cumulative aCCB exposure of 100 mg or more (OR, 2.0; 95% CI, 0.6-6.5). A history of aCCB exposure does not appear to increase hsPDA risk in ELBW infants. Studies using neonatal serum nifedipine concentrations after antenatal exposure should be performed to confirm this conclusion.

Management of preterm labor: atosiban or nifedipine?

Preterm birth is strongly associated with neonatal death and long-term neurological morbidity. The purpose of tocolytic drug administration is to postpone threatening preterm delivery for 48 hours to allow maximal effect of antenatal corticosteroids and maternal transportation to a center with specialized neonatal care facilities. There is uncertainty about the value of atosiban (oxytocin receptor antagonist) and nifedipine (calcium channel blocker) as first-line tocolytic drugs in the management of preterm labor. For nifedipine, concerns have been raised about unproven safety, lack of placebo-controlled trials, and its off-label use. The tocolytic efficacy of atosiban has also been questioned because of a lack of reduction in neonatal morbidity. This review discusses the available evidence, the pros and cons of either drug and aims to provide information to support a balanced choice of first-line tocolytic drug: atosiban or nifedipine?

Nifedipine-induced changes in the electrohysterogram of preterm contractions: feasibility in clinical practice

Objective. Evaluating changes in the power spectral density (PSD) peak frequency of the electrohysterogram (EHG) caused by nifedipine in women with preterm contractions. Methods. Calculation of the PSD peak frequency in EHG contraction bursts at different times of nifedipine treatment in women in gestational age 24 to 32 weeks with contractions. Results. A significant (P < .05) decrease of PSD peak frequency between EHG signals measured before and 15 minutes after administration of nifedipine. A significant (P < .05) decrease in PSD peak frequency comparing signals recorded within 24 hours after administration of nifedipine to signals 1 day after tocolytic treatment. A higher average PSD peak frequency for patients delivering within 1 week than that for patients delivering after 1 week from nifedipine treatment (P > .05). Conclusions. EHG signal analysis has great potential for quantitative monitoring of uterine contractions. Treatment with nifedipine leads to a shift to lower PSD peak frequency in the EHG signal.

Cost-effectiveness of fibronectin testing in a triage in women with threatened preterm labor: alleviation of pregnancy outcome by suspending tocolysis in early labor (APOSTEL-I trial)

Background

At present, women with threatened preterm labor before 32 weeks of gestation are, after transfer to a perinatal center, treated with tocolytics and corticosteroids. Many of these women are treated unnecessarily. Fibronectin is an accurate predictor for the occurrence of preterm birth among women with threatened preterm labor. We will assess whether triage of these women with fibronectin testing, cervical length or their combination is cost-effective.

Methods/Design

We will investigate a prospective cohort of women referred to a perinatal centre for spontaneous threatened preterm labor between 24 and 34 weeks with intact membranes. All women will be tested for fibronectin and cervical length. Women with a cervical length <10 mm and women with a cervical length between 10-30 mm in combination with a positive fibronectin test will be treated with tocolytics according to local protocol. Women with a cervical length between 10-30 mm in combination with a negative fibronectin test will be randomised between treatment with nifedipine (intervention) and placebo (control) for 48 hours. Women with a cervical length > 30 mm will be managed according to local protocol. Corticosteroids may be given to all women at the discretion of the attending physician. Primary outcome measure will be delivery within 7 days. Secondary outcome measures will be neonatal morbidity and mortality, complications of tocolytics, costs and health related quality of life. The analysis will be according to the intention to treat principle. We anticipate the probability on preterm birth within 7 days in the group of women with a negative fibronectine test to be 5%. Two groups of 110 women will be needed to assure that in case of non-inferiority the difference in the proportion of preterm deliveries < 7 days will be within a prespecified boundary of 7.5% (one sided test, β 0.2, α 0.05). Data obtained from women with a positive and negative fibronectin tests in both the cohort study and the trial will be integrated in a cost-effectiveness analysis that will assess economic consequences of the use of fibronectin.

Discussion

This study will provide evidence for the use of fibronectin testing as safe and cost-effective method in a triage for threatened preterm labor.

Trial registration

Nederlands Trial Register (NTR) number 1857, .

Modification of the effect of nifedipine in the pregnant rat myometrium: the influence of progesterone and terbutaline

AIMS

The aims of the study were to investigate the effects of nifedipine on potassium chloride (KCl)-evoked rat uterine contractions on different days of pregnancy in vitro, and the alterations in the effects of nifedipine on combination with terbutaline or progesterone.

MAIN METHODS

In rat myometrial rings taken on different days of pregnancy, rhythmic contractions were evoked with KCl in an isolated organ bath.

KEY FINDINGS

The relaxing effect of nifedipine was most expressed in the 25 mM KCl-induced uterine contractions, reaching the maximum on the last day of pregnancy (day 22). This effect was decreased by progesterone pretreatment in vivo. Synergism was observed in the uterus-relaxing effect of nifedipine+terbutaline, though the extent of potentiation depended on the sequence of administration of the two compounds. When terbutaline was added first in a single dose, the maximal inhibitory effect of nifedipine was lower. This decrease in the inhibition was suspended by a Ca(2+)-poor buffer, indicating the role of Ca(2+) channel activating effect of terbutaline.

SIGNIFICANCE

It is concluded that the uterus-relaxing effect of nifedipine is weakened by progesterone and may be enhanced by low concentrations of beta-mimetics. However, the administration of terbutaline cannot precede the administration of nifedipine.

Differences in the quantal release of catecholamines in chromaffin cells of rat embryos and their mothers

Studies on the bulk catecholamine release from fetal and neonatal rat adrenals, adrenal slices, or isolated chromaffin cells stimulated with high K+, hypoxia, hypercapnia, or acidosis are available. However, a study analyzing the kinetics of quantal secretion is lacking. We report here such a study in which we compare the quantal release of catecholamines from immature rat embryo chromaffin cells (ECCs) and their mothers' (MCCs). Cell challenging with a strong depolarizing stimulus (75 mM K+) caused spike bursts having the following characteristics. ECCs released more multispike events and wave envelopes than MCCs. This, together with narrower single-spike events, a faster decay, and a threefold smaller quantal size suggest a faster secretory machinery in ECCs. Furthermore, with a milder stimulus (25 mM K+) enhanced Ca2+ entry by L-type Ca2+ channel activator BAY K 8644 did not change the kinetic parameters of single spikes in ECCs; in contrast, augmentation of Ca2+ entry increased spike amplitude and width, quantal size, and decay time in MCCs. This suggests that in mature MCCs, the last exocytotic steps are more tightly regulated than in immature ECCs. Finally, we found that quantal secretion was fully controlled by L-type voltage-dependent Ca2+ channels (VDCCs) in ECCs, whereas both L- and non-L VDCCs (N and PQ) contributed equally to secretion control in MCCs. Our results have the following physiological, pharmacological, and clinical relevance: 1) they may help to better understand the regulation of adrenal catecholamine release in response to stress during fetal life and delivery; 2) if clinically used, L-type Ca2+ channel blockers may augment the incidence of sudden infant death syndrome (SIDS); and 3) so-called Ca2+ promotors or activators of Ca2+ entry through L-type VDCCs may be useful to secure a healthy catecholamine surge upon violent stress during fetal life, at birth, or to prevent the SIDS in neonates at risk.

Anaesthesiological considerations on tocolytic and uterotonic therapy in obstetrics

AIM

Significant side effects of tocolytic and uterotonic substances may be of concern to the anaesthesiologist. Recently, new drugs have been introduced having less side effects for both the mother and the neonate.

METHODS

A literature search was undertaken mainly focusing on meta-analyses, to review the possible side effects that might affect the course of anaesthesia and to suggest which precautions should be considered to prevent the occurrence of significant interactions with anaesthetic manipulations and drugs.

RESULTS

Magnesium sulphate has a proven benefit in lowering systolic blood pressure and preventing the occurrence of eclampsia, but not as a tocolytic. beta-adrenergic agonists are being abandoned due to the availability of tocolytic agents causing less side effects. Calcium channel blockers (CCB) are frequently used but can cause major maternal cardiovascular complications. Nitroglycerin seems to be appreciated as an acute tocolytic rather than a routine substance during pre-term labour. Cyclo-oxygenase-2 inhibitors are still under investigation but their tocolytic benefit is questionable mainly due to foetal side effects. Atosiban is considered the first-choice tocolytic. With respect to oxytocic drugs, oxytocine, prostaglandines and methylergometrine may all cause serious side effects especially when combined. The cardiovascular side effects of prostaglandins and methylergometrine can be life-threatening. Both oxytocin and carbetocin have a rather low risk for maternal complications.

CONCLUSION

Atosiban and CCB are at least as effective tocolytic agents as beta-mimetics but have significantly less side effects. Magnesium sulphate can cause neuromuscular blockade, especially when combined with CCB. Concerning oxytocic agents, short-acting oxyctocin and long-acting carbetocin have the least side effects as compared with prostaglandins and methylergometrine.

Adverse drug reactions to tocolytic treatment for preterm labour: prospective cohort study

OBJECTIVE

To evaluate the incidence of serious maternal complications after the use of various tocolytic drugs for the treatment of preterm labour in routine clinical situations.

DESIGN

Prospective cohort study.

SETTING

28 hospitals in the Netherlands and Belgium.

PARTICIPANTS

1920 consecutive women treated with tocolytics for threatened preterm labour.

MAIN OUTCOME MEASURES

Maternal adverse events (those suspected of being causally related to treatment were considered adverse drug reactions) leading to cessation of treatment.

RESULTS

An independent panel evaluated the recorded adverse events, without knowledge of the type of tocolytic used. Of the 1920 women treated with tocolytics, 1327 received a single course of treatment (69.1%), 282 sequential courses (14.7%), and 311 combined courses (16.2%). Adverse drug reactions were categorised as serious or mild in 14 cases each. The overall incidence of serious adverse drug reaction was 0.7%. Compared with atosiban, the relative risk of an adverse drug reaction for single treatment with a beta adrenoceptor agonist was 22.0 (95% confidence interval 3.6 to 138.0) and for single treatment with a calcium antagonist was 12 (1.9 to 69). Multiple drug tocolysis led to five serious adverse drug reactions (1.6%). Multiple gestation, preterm rupture of membranes, and comorbidity were not independent risk factors for adverse drug reactions.

CONCLUSIONS

The use of beta adrenoceptor agonists or multiple tocolytics for preventing preterm birth is associated with a high incidence of serious adverse drug reactions. Indometacin and atosiban were the only drugs not associated with serious adverse drug reactions. A direct comparison of the effectiveness of nifedipine and atosiban in postponing preterm delivery is needed.

The relaxant effect of nifedipine in human uterine smooth muscle and the BK(Ca) channel

OBJECTIVE

The purpose of this study was to investigate the effects of K+ channel blockade on the uterorelaxant effects of nifedipine in human myometrium during pregnancy.

STUDY DESIGN

Biopsies of human myometrium were obtained at elective cesarean section (n = 24). Dissected myometrial strips suspended under isometric conditions, undergoing spontaneous and oxytocin-induced contractions, were subjected to K+ channel blockade using tetraethylammonium (TEA) or iberiotoxin (IbTX) followed by cumulative additions of nifedipine (1 nmol/L-10 micromol/L). Control experiments were run simultaneously. Integrals of contractile activity were measured using the PowerLab hardware unit and Chart v3.6 software. Data were analyzed using one-way analysis of variance (ANOVA) followed by post hoc analysis.

RESULTS

Nifedipine exerted a potent and cumulative inhibitory effect on spontaneous contractions and oxytocin-induced contractions in human myometrium in vitro, in comparison to control measurements (P < .05, n = 6). Incubation of strips with TEA or IbTX, prior to addition of nifedipine, significantly attenuated the relaxant effect exerted by nifedipine (P < .05, n = 6).

CONCLUSION

This study demonstrates that the uterorelaxant effect of nifedipine is attenuated by potassium channel (K+) blockade. This suggests that K+ channel conductance, and particularly the BK(Ca) channel, plays a role in the potent relaxant effect of nifedipine, hitherto presumed to act solely through L-gated calcium channels.