Pregnancy outcome after gestational exposure to amiodarone in Canada

Fetal pharmacotherapy

Rapid progress has recently been encountered in pharmacologically treating the unborn baby. This unique area of drug therapy raises new methodological and ethical questions. This article is a systematic review of known modalities of fetal pharmacotherapy, and aims to highlight essential principles, difficulties and controversies in fetal pharmacotherapy. Unique pharmacokinetic features of pregnancy, the placenta and the fetus govern maternal-to-fetal drug transfer. Ethically, it is important that the mother and family are appropriately informed about the evidence in favour of specific fetal therapy, its risks and alternatives. Antenatal use of corticosteroids for lung maturation is an example of adequate methodology, leading to clear results. In contrast, the initial hopes in antenatal use of phenobarbital were based on less than optimal methodology. Folic acid for the prevention of neural tube defects is the first instance of fetal therapy that has led to the prevention of a major malformation. Serious infections, such as HIV, Group B streptococcus and toxoplasmosis highlight the need for controlled, randomised studies to prevent fetal infection. With scores of new modalities of fetal therapy likely to be introduced in the next few years, it will be important to adhere to the best possible methodology and execution, in order to address optimally the needs of the fetus.

The effects of amiodarone on the thyroid

Amiodarone is a benzofuranic-derivative iodine-rich drug widely used for the treatment of tachyarrhythmias and, to a lesser extent, of ischemic heart disease. It often causes changes in thyroid function tests (typically an increase in serum T(4) and rT(3), and a decrease in serum T(3), concentrations), mainly related to the inhibition of 5'-deiodinase activity, resulting in a decrease in the generation of T(3) from T(4) and a decrease in the clearance of rT(3). In 14-18% of amiodarone-treated patients, there is overt thyroid dysfunction, either amiodarone-induced thyrotoxicosis (AIT) or amiodarone-induced hypothyroidism (AIH). Both AIT and AIH may develop either in apparently normal thyroid glands or in glands with preexisting, clinically silent abnormalities. Preexisting Hashimoto's thyroiditis is a definite risk factor for the occurrence of AIH. The pathogenesis of iodine-induced AIH is related to a failure to escape from the acute Wolff-Chaikoff effect due to defects in thyroid hormonogenesis, and, in patients with positive thyroid autoantibody tests, to concomitant Hashimoto's thyroiditis. AIT is primarily related to excess iodine-induced thyroid hormone synthesis in an abnormal thyroid gland (type I AIT) or to amiodarone-related destructive thyroiditis (type II AIT), but mixed forms frequently exist. Treatment of AIH consists of L-T(4) replacement while continuing amiodarone therapy; alternatively, if feasible, amiodarone can be discontinued, especially in the absence of thyroid abnormalities, and the natural course toward euthyroidism can be accelerated by a short course of potassium perchlorate treatment. In type I AIT the main medical treatment consists of the simultaneous administration of thionamides and potassium perchlorate, while in type II AIT, glucocorticoids are the most useful therapeutic option. Mixed forms are best treated with a combination of thionamides, potassium perchlorate, and glucocorticoids. Radioiodine therapy is usually not feasible due to the low thyroidal radioiodine uptake, while thyroidectomy can be performed in cases resistant to medical therapy, with a slightly increased surgical risk.

Effects of amiodarone administration during pregnancy on neonatal thyroid function and subsequent neurodevelopment

Amiodarone, a benzofuranic derivative, iodine-rich drug, has been used in pregnancy for either maternal or fetal tachyarrhythmias. Amiodarone, its main metabolite (desethylamiodarone) and iodine are transferred, albeit incompletely, through the placenta, resulting in a relevant fetal exposure to the drug and iodine overload. Since the fetus acquires the capacity to escape from the acute Wolff-Chaikoff effect only late in gestation, the iodine overload may cause fetal/neonatal hypothyroidism and goiter. Among the reported 64 pregnancies in which amiodarone was given to the mother, 11 cases (17%) of hypothyroidism in the progeny (10 detected at birth, 1 in utero) were reported, 9 non-goitrous (82%) and 2 (18%) associated with goiter. Hypothyroidism was transient in all cases, and only 5 infants were treated short-term with thyroid hormones. Only 2 newborns had transient hyperthyroxinemia, associated with low serum TSH concentrations in one. Neurodevelopment assessment of the hypothyroid infants, when carried out, showed in some instances mild abnormalities, most often reminiscent of the Non-verbal Learning Disability Syndrome; however, these features were also reported in some amiodarone-exposed euthyroid infants, suggesting that there might be a direct neurotoxic effect of amiodarone during fetal life. Breast-feeding was associated with a substantial ingestion of amiodarone by the infant, but in the few cases followed it did not cause changes in the newborn's thyroid function. In conclusion, amiodarone therapy during pregnancy may cause fetal/neonatal hypothyroidism and, less frequently, goiter. Thus, the use of amiodarone in pregnancy should be limited to maternal/fetal tachyarrhythmias which are resistant to other drugs or life-threatening. If amiodarone is used during gestation, a careful fetal/neonatal evaluation of thyroid function and morphology is warranted. It seems prudent to advise that fetal/neonatal hypothyroidism be treated, as soon as the diagnosis is made, even in utero, to avoid neurodevelopment abnormalities, although the latter may occur independently of hypothyroidism. If breast-feeding is allowed, careful evaluation of the infant's thyroid function and morphology is required because of the continuing exposure of the infant to the drug.

Antiarrhythmic drugs in pregnancy

During pregnancy a number of rhythm disturbances can occur in both the mother and fetus; these may range from benign ectopy to life-threatening arrhythmias. With a clear understanding of the maternal hemodynamic changes associated with pregnancy, and the appropriate antiarrhythmic therapies available, almost all such cases can be treated successfully. Although no drug is completely safe, most are well tolerated and can be given with relatively low risk. Drug therapy should be avoided during the first trimester of pregnancy if possible and drugs with the longest record of safety should be used as first-line therapy. Conservative therapies should be used when appropriate. Several drug options exist for most maternal and fetal arrhythmias.

Neonatal bradycardia

Heart rate monitoring has become a ubiquitous part of fetal and neonatal assessment, and has made detection of bradycardia in the fetal and neonatal periods a frequent occurrence. Evaluation of a fetus or neonate with bradycardia requires an understanding of the mechanisms of bradycardia as well as the cardiac and non-cardiac causes of bradycardia. The mechanisms of bradycardia include sinus bradycardia, abnormalities of sinus node function and abnormalities of atrioventricular conduction. In the instances where sinus bradycardia is pathologic, it usually results from non-cardiac disease. Sinus node dysfunction is rare early in life but can arise from surgical interventions, congenital heart disease, or endovascular manipulations. Abnormalities of atrioventricular conduction have a similar etiology but are more common than sinus node disease. Atrioventricular nodal disease can also result from maternal collagen vascular disease, even in the absence of symptoms in the mother. In these cases, epidemiological issues such as heart block in subsequent pregnancies and the maternal risk of developing symptomatic collagen vascular disease become important. The approach to treatment and long-term prognosis for bradycardia in the neonate is highly dependent on the underlying etiology and on the presence of concurrent factors such as structural heart disease.

Neurodevelopment after in utero amiodarone exposure

It is not known whether amiodarone is neurotoxic to the fetus, as it is to adults. We evaluated neurodevelopment of a historical cohort (N = 10) of children exposed transplacentally to amiodarone. Scores on standardized tests of cognitive and language skills were compared (by Wilcoxon signed rank test) between eight toddlers and matched controls. It was not possible to obtain controls for older amiodarone-exposed children (aged 9.7 and 12.0 years), whose test results were compared descriptively with normative data. There was no difference in IQ scores between amiodarone-exposed toddlers and controls. All had favorable temperaments. However, amiodarone-exposed toddlers showed expressive language skills that were relatively poorer than verbal skills, when compared with controls (p = 0.046). One amiodarone-exposed toddler exhibited global developmental delay. The older amiodarone-exposed children had well-developed social competence, favorable global IQ scores, but problems with reading comprehension, written language, and arithmetic. This picture is reminiscent of the Nonverbal Learning Disability Syndrome. There may be neurotoxicity associated with transplacental exposure to amiodarone. Follow-up is warranted, although most mothers were happy with the development of their children.

Transient neonatal hypothyroidism after gestational exposure to amiodarone: a follow-up of two cases

Amiodarone (AMD) is an antiarrhythmic drug which contains 37% of iodine. It can reach the fetus by transplacental passage and induce fetal hypothyroidism. Since in some pregnant women AMD represents a cardinal therapeutic opportunity, it is necessary to establish not only the risk of teratogenicity linked to fetal AMD exposure but also to evaluate the psychomotor development of children with neonatal thyroid dysfunction related to fetal AMD exposure. We report on two cases involving children with an AMD gestational exposure and transient neonatal hypothyroidism, who were followed-up until the age of 4 years 8 months and 5 years 6 months, respectively. Denver's developmental milestone test and Whechsler Preschool and Primary Scale of Intelligence (WPPSI) were administered to the patients in accordance to their age. A normal psychomotor development was observed in both patients with full scale IQ score, verbal and performance IQ scores within normal range. In conclusion, if these data were validated by larger studies, it might not be obligatory to discontinue AMD administration in cardiopathic pregnant women, since mental impairment may not necessarily occur in children with transient neonatal hypothyroidism caused by fetal AMD exposure. However, the evaluation of the thyroid function of these children is imperative.

Management of hypothyroidism during pregnancy

Hypothyroidism during pregnancy occurs in 1/1600-2000 deliveries, according to the most recent publications. The most common causes are chronic autoimmune thyroid disease, radiodine-131 treatment, or surgical removal. The diagnosis is difficult to make on clinical grounds alone, even in advanced cases, and a high index of suspicion is needed. Some women are at high risk of developing hypothyroidism, and they should be screened. These women may have had previous treatment for hyperthyroidism; high-dose neck irradiation, evidence of thyroid autoimmunity, amiodarone therapy, suspected hypopituitarism, and type I diabetics. The best laboratory test is the serum TSH, followed, if elevated, by a free T4 index and a TPO-ab titer. Thyroid antibodies have been associated with an increased (double) risk of miscarriage and postpartum thyroiditis. Frequent (22-44%) pregnancy-induced hypertension leading to preterm delivery, and prematurity is the main complication observed in those still hypothyroid near term. Proper therapy eliminates or reduces the risk. No congenital anomalies have been reported in the most recent studies, and the data available shows that both physical and mental development have been normal until children are 10 years old. However, one study reported lower IQs in children of euthyroid women with positive TPO-ab than in children of TPO-ab negative mothers. Levothyroxine is the treatment of choice. Euthyroidism must be reached and maintained in a timely fashion. Many women need more thyroxine during pregnancy, and surveillance of thyroid function is needed throughout gestation to make dose adjustments when needed. During the postpartum periods the thyroxine requirements decrease to preconception levels.

Alteration of human placental vascular tone by antiarrhythmic medications in vitro

INTRODUCTION

Antiarrhythmic medications are commonly used during pregnancy for treatment of maternal or fetal arrhythmias, but little is known about their effect on human placental vascular tone and, consequently, placental blood flow. The objective of this study was to evaluate the tone responses caused by antiarrhythmic medications in human placental vessels from normal term pregnancies in vitro.

METHODS AND RESULTS

Isolated human placental arteries and veins from uncomplicated term pregnancies incubated in Krebs'-bicarbonate under 5% oxygen/5% carbon dioxide/balance nitrogen (PO2 35 to 38 torr) were exposed to cumulative doses of quinidine, procainamide, lidocaine, flecainide, propranolol, amiodarone, verapamil, digoxin, and adenosine after submaximal contraction with 5-hydroxytryptamine. The study was conducted both in the presence and absence of endothelium. The addition of the tested medications caused a significant, dose-dependent relaxation of human placental arteries and veins except for adenosine, which induced a sustained, dose-dependent contraction of human placental vessels regardless of the presence or absence of tone. Removal of the endothelium did not alter these responses.

CONCLUSIONS

Based on these results, the medications tested should have no decremental effect on placental blood flow, with the possible exception of adenosine, which causes significant, dose-dependent contraction of human placental vessels in vitro. Should similar contraction be present in vivo, it may have an adverse effect on the fetus when administering adenosine to pregnant women at term or during labor.