Digoxin, flecainide, and amiodarone transfer across the placenta and the effects of an elevated umbilical venous pressure on the transfer rate

2023 HRS expert consensus statement on the management of arrhythmias during pregnancy

This international multidisciplinary expert consensus statement is intended to provide comprehensive guidance that can be referenced at the point of care to cardiac electrophysiologists, cardiologists, and other health care professionals, on the management of cardiac arrhythmias in pregnant patients and in fetuses. This document covers general concepts related to arrhythmias, including both brady- and tachyarrhythmias, in both the patient and the fetus during pregnancy. Recommendations are provided for optimal approaches to diagnosis and evaluation of arrhythmias; selection of invasive and noninvasive options for treatment of arrhythmias; and disease- and patient-specific considerations when risk stratifying, diagnosing, and treating arrhythmias in pregnant patients and fetuses. Gaps in knowledge and new directions for future research are also identified.

Frequency of differential placental transfer to twins of maternal antiretroviral medications

BACKGROUND

Placental passage of drugs in twins is poorly understood, and is unknown regarding antiretrovirals (ARVs). In the event of large differences in the exposure of 2 twins to the same maternal therapy, this could have a clinical impact in terms of prevention of perinatal HIV transmission or adverse effects.

OBJECTIVE

To describe the frequency of differential transplacental passage of antiretrovirals between twins.

STUDY DESIGN

The study was performed retrospectively, on data from women included in a multicenter perinatal HIV cohort study. All twin pairs for which the mother received antiretroviral therapy and for which drug concentrations in both of the umbilical cords after cord clamping at delivery were studied. We considered that a difference in concentrations of more than 50 % between twins was a substantial difference (ratios below 0.67 or above 1.50).

RESULTS

We analyzed 29 twin pairs, 27 dichorionic and 2 monochorionic diamniotic. Cord blood concentrations differed between the 2 twins by more than 50 % for at least one ARV in 9 twin pairs, 8 dichorionic and 1 monochorionic. Discordant concentrations were observed in one or more cases for several nucleoside reverse transcriptase inhibitors (tenofovir, emtricitabine, lamivudine, zidovudine) and protease inhibitors (atazanavir, lopinavir, saquinavir et ritonavir); within individual twin pairs placental transfer was discordant for one or more ARVs, but identical for others.

CONCLUSION

Concentrations differed in nearly one third of twin pairs. This may be due to interindividual genetic variability of placental transporters between dizygotic twins as well as physiological differences between twins.

Successful in utero transesophageal pacing for severe drug-resistant tachyarrhythmia

Sustained fetal tachyarrhythmia can evolve into a life-threatening condition in 40% of cases when hydrops develops, with a 27% risk of perinatal death. Several antiarrhythmic drugs can be given solely or in combination to the mother to achieve therapeutic transplacental concentrations. Therapeutic failure could lead to progressive cardiac insufficiency and restrict therapeutic options to either elective delivery or direct fetal administration of antiarrhythmic drugs, which may increase the risk of death. We report for the first time successful fetal transesophageal pacing to treat a hydropic fetus with drug-resistant tachyarrhythmia.

Pharmacotherapy in pregnancy; effect of ABC and SLC transporters on drug transport across the placenta and fetal drug exposure

Pharmacotherapy during pregnancy is often inevitable for medical treatment of the mother, the fetus or both. The knowledge of drug transport across placenta is, therefore, an important topic to bear in mind when deciding treatment in pregnant women. Several drug transporters of the ABC and SLC families have been discovered in the placenta, such as P-glycoprotein, breast cancer resistance protein, or organic anion/cation transporters. It is thus evident that the passage of drugs across the placenta can no longer be predicted simply on the basis of their physical-chemical properties. Functional expression of placental drug transporters in the trophoblast and the possibility of drug-drug interactions must be considered to optimize pharmacotherapy during pregnancy. In this review we summarize current knowledge on the expression and function of ABC and SLC transporters in the trophoblast. Furthermore, we put this data into context with medical conditions that require maternal and/or fetal treatment during pregnancy, such as gestational diabetes, HIV infection, fetal arrhythmias and epilepsy. Proper understanding of the role of placental transporters should be of great interest not only to clinicians but also to pharmaceutical industry for future drug design and development to control the degree of fetal exposure.

Active transport across the human placenta: impact on drug efficacy and toxicity

The human placenta expresses a large number of transport proteins. The ATP-binding cassette (ABC) family of active efflux pumps, predominantly localised to the maternal-facing syncytial membrane of placental microvilli, comprise the major placental drug efflux transporters. A variety of other transporters are also expressed in the placenta that can facilitate xenobiotic transfer in both the maternal and fetal directions. Many drugs administered in pregnancy are ABC transporter substrates, and many are either teratogenic or fetotoxic. The in vitro, in vivo and clinical evidence reviewed in this article argues that active efflux of drugs by placental transporters helps to maintain its barrier function, reducing the incidence of adverse fetal effects. ABC transporter polymorphisms may explain the wide variability observed in fetal drug concentrations, incidence of teratogenesis or drug failure in pregnancies exposed to therapeutic agents. Although our understanding of the molecular mechanics and dynamics of placental drug transfer is advancing, much work is needed to fully appreciate the significance of placental drug transporters in the face of increasing drug administration in pregnancy.

Role of placental ATP-binding cassette (ABC) transporters in antiretroviral therapy during pregnancy

Highly active anti-retroviral therapy (HAART) is used to treat HIV-infected patients and involves administration of multiple antiretroviral drugs acting at different steps of the HIV life cycle. In treating HIV-infected pregnant patients, the aim of therapy is not only to treat the mother but also to prevent the transmission of the virus to the fetus. Among the antiretroviral drugs used, there are differences in the extent of transfer of these drugs across the placenta; HIV protease inhibitors are particularly poorly transferred. Activities of ABC transporters expressed in the human placenta as well as differences in plasma protein binding may account for the poor transplacental transfer of certain drugs. This review discusses factors affecting the extent of placental transfer of antiretroviral drugs during pregnancy. These issues may also apply to drugs in other therapeutic categories.

Drug Transfer and Metabolism by the Human Placenta

The major function of the placenta is to transfer nutrients and oxygen from the mother to the foetus and to assist in the removal of waste products from the foetus to the mother. In addition, it plays an important role in the synthesis of hormones, peptides and steroids that are vital for a successful pregnancy. The placenta provides a link between the circulations of two distinct individuals but also acts as a barrier to protect the foetus from xenobiotics in the maternal blood. However, the impression that the placenta forms an impenetrable obstacle against most drugs is now widely regarded as false. It has been shown that that nearly all drugs that are administered during pregnancy will enter, to some degree, the circulation of the foetus via passive diffusion. In addition, some drugs are pumped across the placenta by various active transporters located on both the fetal and maternal side of the trophoblast layer. It is only in recent years that the impact of active transporters such as P-glycoprotein on the disposition of drugs has been demonstrated. Facilitated diffusion appears to be a minor transfer mechanism for some drugs, and pinocytosis and phagocytosis are considered too slow to have any significant effect on fetal drug concentrations. The extent to which drugs cross the placenta is also modulated by the actions of placental phase I and II drug-metabolising enzymes, which are present at levels that fluctuate throughout gestation. Cytochrome P450 (CYP) enzymes in particular have been well characterised in the placenta at the level of mRNA, protein, and enzyme activity. CYP1A1, 2E1, 3A4, 3A5, 3A7 and 4B1 have been detected in the term placenta. While much less is known about phase II enzymes in the placenta, some enzymes, in particular uridine diphosphate glucuronosyltransferases, have been detected and shown to have specific activity towards marker substrates, suggesting a significant role of this enzyme in placental drug detoxification. The increasing experimental data on placental drug transfer has enabled clinicians to make better informed decisions about which drugs significantly cross the placenta and develop dosage regimens that minimise fetal exposure to potentially toxic concentrations. Indeed, the foetus has now become the object of intended drug treatment. Extensive research on the placental transfer of drugs such as digoxin and zidovudine has assisted with the safe treatment of the foetus with these drugs in utero. Improved knowledge regarding transplacental drug transfer and metabolism will result in further expansion of pharmacological treatment of fetal conditions.

Fetal supraventricular tachycardia: a role for amiodarone as second-line therapy?

OBJECTIVE

The aim of this study was to evaluate the role of amiodarone for the prenatal treatment of hydropic fetuses with supraventricular tachycardia.

METHODS

A group of 26 hydropic fetuses with supraventricular tachycardia was studied retrospectively.

RESULTS

Twenty-five fetuses received transplacental treatment. The overall prenatal conversion rate was 60%. Nine fetuses were converted to sinus rhythm using either flecainide (n = 7) or amiodarone (n = 2) as first line therapy, whilst digoxin alone or in association with sotalol failed to restore sinus rhythm in all cases. After first-line therapy, supraventricular tachycardia persisted in 10 fetuses. Nine fetuses received amiodarone alone or in association with digoxin as second-line therapy, five of whom were converted to sinus rhythm. Among the 11 live neonates treated by amiodarone in utero, 2 (17%) presented an elevated thyroid stimulating hormone at day 3-4. These two infants received thyroid hormone substitution therapy and had a normal outcome.

CONCLUSION

When first-line therapy fails to restore sinus rhythm in hydropic fetuses with supraventricular tachycardia, amiodarone therapy should be considered as it allows a substantial number of fetuses to be converted prenatally.