Tocolysis and preterm labour

Nanomedicine strategies to improve therapeutic agents for the prevention and treatment of preterm birth and future directions

The World Health Organisation (WHO) estimates 15 million babies worldwide are born preterm each year, with 1 million infant mortalities and long-term morbidity in survivors. Whilst the past 40 years have provided some understanding in the causes of preterm birth, along with development of a range of therapeutic options, notably prophylactic use of progesterone or uterine contraction suppressants (tocolytics), the number of preterm births continues to rise. Existing therapeutics used to control uterine contractions are restricted in their clinical use due to pharmacological drawbacks such as poor potency, transfer of drugs to the fetus across the placenta and maternal side effects from activity in other maternal systems. This review focuses on addressing the urgent need for the development of alternative therapeutic systems with improved efficacy and safety for the treatment of preterm birth. We discuss the application of nanomedicine as a viable opportunity to engineer pre-existing tocolytic agents and progestogens into nanoformulations, to improve their efficacy and address current drawbacks to their use. We review different nanomedicines including liposomes, lipid-based carriers, polymers and nanosuspensions highlighting where possible, where these technologies have already been exploited e.g. liposomes, and their significance in improving the properties of pre-existing therapeutic agents within the field of obstetrics. We also highlight where active pharmaceutical agents (APIs) with tocolytic properties have been used for other clinical indications and how these could inform the design of future therapeutics or be repurposed to diversify their application such as for use in preterm birth. Finally we outline and discuss the future challenges.

Nifedipine versus ritodrine during external cephalic version procedure: a case control study

OBJECTIVE

Published series regarding interventions for facilitating external cephalic version (ECV) have concluded that parenterally administered beta-stimulant tocolytics, increased ECV success rate and reduced the number of cesarean sections. However, there were insufficient data regarding calcium channel blockers to provide good evidence regarding its efficacy. Given the paucity of literature, we aimed to compare the efficacy of nifedipine to that of ritodrine on ECV success rates.

METHODS

This is a retrospective case control study of prospectively collected data of patients who underwent ECV between January 2012 and December 2013 at Bikur Cholim Medical Center and Hadassah-Hebrew University Medical Center in Jerusalem, Israel. Patient undergoing ECV with tocolysis by ritodrine were compared with those using nifedipine as tocolysis. Patients were matched in a one-to-one ration by parity and placental location.

RESULTS

Overall, 148 women received ritodrine and 148 women received nifedipine before ECV procedure. Overall success rate was higher among the ritodrine group (82.4 vs. 63.5%, p < .001). Among nulliparous and among parous, success rate was higher in the ritodrine group (78.9 vs. 57.9 and 88.6 vs. 73.5%, p = .001, p = .04, respectively). Vaginal delivery rate was higher among the ritodrine group (86.5 vs. 68.9%, p < .001). Cesarean delivery rate was 31.1% for the nifedipine group versus 13.5% in the ritodrine group (p < .001). Number needed to treat to benefit (NNTb) 5.7 (95% confidence interval 3.7-12.1). Overall, 216 of 296 (72.9%) of ECV were successful. Ritodrine was associated with higher success rates as compared with nifedipine (56.5 vs. 32.5%, p < .001). In a multivariate analysis, ritodrine tocolytic therapy was independently associated higher ECV success rates as compared to nifedipine (OR 4.54, 95% CI 2.38-9.09). Higher amniotic fluid index (OR 1.16, 95% CI 1.05-1.28) and nulliparity (OR 0.16, 95% CI 0.08-0.30) were additional independent predictors of ECV outcome.

CONCLUSION

Ritodrine significantly improve the success of ECV compared with nifedipine. Both drugs are shown to be safe.

Systematic review and meta-analysis of randomized controlled trials of atosiban versus nifedipine for inhibition of preterm labor

BACKGROUND

Two tocolytic drugs-atosiban and nifedipine-are currently used for first-line treatment of preterm labor (PTL).

OBJECTIVE

To compare the efficacy and safety of atosiban with nifedipine for PTL treatment.

SEARCH STRATEGY

In May 2017, we searched PubMed, Scopus, Web of Science, and Cochrane Central Register of Controlled Clinical Trials with search terms including "nifedipine", "atosiban", and "preterm labor".

SELECTION CRITERIA

Randomized controlled trials of women with PTL.

DATA COLLECTION AND ANALYSIS

Data were extracted for study design, patient characteristics, risk of bias domains, and study outcomes. A random-effects model was used to generate pooled risk ratios (RRs) and 95% confidence intervals (CIs).

RESULTS

We included seven studies that enrolled 992 patients. There was no significant difference between atosiban and nifedipine for pregnancy prolongation of 48 hours or more regarding efficacy (RR 1.06, 95% CI 0.92-1.22; P=0.440) or effectiveness (0.93, 0.84-1.03; P=0.177). Pregnancy prolongation for 7 days or more also did not differ between groups for efficacy (RR 1.04, 95% CI 0.89-1.21; P=0.656) or effectiveness (0.91, 0.79-1.05; P=0.177). Atosiban-however-was associated with fewer maternal side-effects than nifedipine.

CONCLUSION

Atosiban resulted in fewer maternal side-effects than nifedipine, with no difference in pregnancy prolongation. PROSPERO registration: CRD42018090223.

The effects of tocolysis on neonatal septic death in women with PPROM: a retrospective cohort study

PURPOSE

In women with preterm premature rupture of membranes (PPROM), particularly those with suspected chorioamnionitis, the benefit of tocolysis on neonatal outcome remains unclear. Our purpose was to evaluate the effect of tocolysis on neonatal septic death in women with PPROM with and without chorioamnionitis.

METHODS

A retrospective cohort study was used to address our study objective. We created a cohort consisting of all live births between 24 and 32 weeks' gestation that were registered in the Linked Birth and Infant Death data files (2009-2013) from the United States. Multivariate logistic regression was used to evaluate the effect of tocolysis on neonatal septic death at 7 and 28 days in births with and without chorioamnionitis.

RESULTS

Of the 46,968 births that met our inclusion criteria, tocolysis was administered to 6264 (13.3%). Tocolysis was more commonly prescribed to Caucasians, smokers, in multiple birth pregnancies, and to women with a history of preterm births. Tocolysis was not significantly associated with neonatal septic death at 7 days (OR 0.66, 95% CI 0.39-1.13) or at 28 days (OR 0.85, 95% CI 0.60-1.19). This was consistent in pregnancies with and without chorioamnionitis. Furthermore, tocolysis was associated with a reduced risk of neonatal septic death at 7 days when administered between 24 and 27 weeks' gestation (OR 0.44, 95% CI 0.22-0.88).

CONCLUSIONS

In the setting of PPROM, tocolysis does not appear to increase the risk of neonatal septic death at 7 and 28 days. Therefore, consideration should be given to its administration if clinically indicated.

Tocolysis for inhibiting preterm birth in extremely preterm birth, multiple gestations and in growth-restricted fetuses: a systematic review and meta-analysis

This systematic review was to identify available evidence on the effectiveness of tocolysis in inhibiting preterm delivery for women with threatened extremely preterm birth, multiple gestations, and growth-restricted babies, and their infants' outcomes. A comprehensive search using MEDLINE, Embase, the Cochrane Library, CINAHL, POPLINE and the WHO Global Health Library databases was conducted on 14 February 2014. For selection criteria, randomized controlled trials and non-randomized studies that compared tocolysis treatment to placebo or no treatment were considered. Selection of eligible studies, critical appraisal of the included studies, data collection, meta-analyses, and assessment of evidence quality were performed in accordance with the Cochrane Collaboration's guidance and validated assessment criteria. The search identified seven studies for extremely preterm birth, in which three were randomized controlled trials (RCTs) and four were non-randomized studies (non-RCTs). There were no eligible studies identified for women with multiple pregnancy and growth-restricted fetuses. Meta-analyses indicated no significant difference was found for the relative effectiveness of tocolytics versus placebo for prolonging pregnancy in women with extremely preterm birth (RR 1.04, 95% CI 0.83 to 1.31) or reducing the rate of perinatal deaths (RR 2.22, 95% CI 0.26 to 19.24). In summary, there is no evidence to draw conclusions on the effectiveness of tocolytic therapy for women with threatened extremely preterm birth, multiple gestations, and growth-restricted babies.

Comparison of the efficacy and adverse effects of nifedipine and indomethacin for the treatment of preterm labor

OBJECTIVE

To compare the effectiveness and adverse effects of nifedipine versus indomethacin in the treatment of preterm labor.

METHODS

In a randomized clinical trial, 79 women with labor pain at 26-33 weeks of gestation were treated with either oral nifedipine (n=40) or rectal indomethacin (n=39).

RESULTS

Twenty-three (59%) women in the indomethacin group, and 10 (25%) in the nifedipine group did not respond to treatment (P=0.002). None of the 16 and 30 women remaining in the indomethacin and nifedipine groups, respectively, delivered during the subsequent 48 hours. Of these remaining women, 1 (6.25%) in the indomethacin group and 4 (13.3%) in the nifedipine group delivered between 48 hours and 7 days (P=0.162). For the women who responded to treatment, the mean gestational age at time of delivery was 238.5±19.4 days and 246.4±15.4 days in the nifedipine and indomethacin groups, respectively (P=0.182). Seventeen (42.5%) women in the nifedipine group, and 11 (28.2%) in the indomethacin group showed adverse effects (P=0.184).

CONCLUSION

Indomethacin was less effective than nifedipine for the fast treatment of preterm labor. For women who responded to treatment within 2 hours, however, the delaying of delivery by indomethacin was similar to that by nifedipine.

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.

Emerging tocolytics: challenges in designing and testing drugs to delay preterm delivery and prolong pregnancy

The global rate of preterm delivery (before 37 completed weeks of pregnancy) is increasing and there are no effective means available to prevent this rise. Prematurity is the principal cause of neonatal mortality and a major cause of pediatric morbidity and long-term disability. Current strategies to prolong pregnancy are based on inhibiting the mechanisms that effect uterine smooth muscle (myometrium) contractions in women who are in preterm labor. Most drugs in this group were developed for other purposes. Newer strategies are designed to maintain a state of uterine quiescence and pregnancy, preventing the myometrium from initiating contractions and entering preterm labor. Again, it may be possible to use existing drugs for pregnancy maintenance. Several financial and practical barriers exist for developing completely new drugs to delay labor. Designing clinical trials to test tocolytics is complicated, as the health of two patients must be considered and the nature of preterm birth and its outcomes are different at early preterm labor (< 28 weeks) and late preterm labor (34 - 36 weeks).

The present and future of tocolysis

This chapter discusses the tocolytic agents currently in use for the treatment of preterm labour and considers them in light of the evidence base. These agents are the beta2 sympathomimetic agonists, magnesium sulphate (MgSO(4)), indomethacin, nifedipine and atosiban. The available evidence for these agents shows that the beta2 agents are effective but have significant maternal side effects and no effect on perinatal outcome. MgSO(4) and glyceryl trinitrate are clearly ineffective. Nifedipine is effective with a low maternal side effect profile and is associated with improved perinatal outcomes. Meta-analyses of the several randomized controlled trials of atosiban show that it is no more effective than other tocolytic therapies. Possible directions for the future will be discussed.

Terbutaline versus nifedipine for prolongation of pregnancy in patients with preterm labor

OBJECTIVE

To compare the effectiveness, safety, and possible adverse effects of terbutaline and nifedipine in prolonging pregnancy beyond 48 h.

METHODS

A randomized controlled trial was conducted with 174 pregnant women admitted with preterm labor randomized into 2 groups, which were given terbutaline (95 patients) and nifedipine (79 patients), respectively. Bivariate and multivariate analyses, using logistic regression, were used to analyze the data.

RESULTS

No statistically significant difference was found between the 2 groups in terms of prolongation of gestation to 48 h. The failure rate in terms of prolonging gestation for 24 h was found to be 12.6% for the terbutaline group and 10.1% for the nifedipine group, which was not found to be statistically significant (P value=0.61). Side effects were significantly more common in the terbutaline group, except for maternal hypotension.

CONCLUSION

Terbutaline and nifedipine appear to be equally effective in their tocolytic action. However, nifedipine did have the advantage of ease of administration. It also had significantly less effect on the fetal heart rate.

Magnesium ion inhibits spontaneous and induced contractions of isolated uterine muscle

AIM

Magnesium sulfate, mainly used in obstetrics to treat eclamptic convulsions, is currently questioned as to its clinical tocolytic effect. We aimed to study the relaxant action (if any) of magnesium sulfate on in vitro pregnant and non-pregnant myometrium.

METHODS

Myometrial strips, harvested from five pregnant women (35-39 gestational weeks) during Cesarean procedures indicated for dystocia or scared uterus and five non-pregnant women during hysterectomy or myomectomy for benign conditions, were placed in a Krebs-Henseleit solution organ bath and the isometric force was registered. We assessed the effect of Mg2+ (magnesium sulfate) at different concentrations (0.50-10 mM) on spontaneous and oxytocin-induced (1 microM) myometrial contractility.

RESULTS

Mg2+ temporarily reduced spontaneous myometrial contractions in a dose-dependent manner, with efficient regimens at 2.0-2.5 mM, and arrested contractility completely at 3 mM. Oxytocin-induced contractions were reduced by 30-40% at 8 mM and decreased further at 9-10 mM. Induced contractions were reduced, in a dose-dependent and time-dependent manner (maximum effect at 20 min), at higher Mg2+ concentrations and with non-significant proportional differences between pregnant and non-pregnant myometrium.

CONCLUSIONS

The present in vitro study suggests a possible benefit of Mg2+ in the inhibition of spontaneous myometrial contractility, but not of uterine-induced hyperactivity.