Fetal Risk Summary
Esmolol is a short-acting cardioselective b-adrenergic blocking agent that is structurally related to atenolol and metoprolol. The drug is used for the rapid, temporary treatment of supraventricular tachyarrhythmias (e.g., atrial flutter or fibrillation, sinus tachycardia) and for hypertension occurring during surgery. Because hypotension may occur with its useup to 50% of patients in some trialsthe potential for decreased uterine blood flow and resulting fetal hypoxia should be considered.
Reproduction studies in rats with IV doses up to 10 times the maximum human maintenance dose (MHMD) for 30 minutes daily revealed no evidence of embryo or fetal harm (1). Maternal toxicity and lethality were evident at 33 times the MHMD. Studies in pregnant rabbits with nonmaternal toxic doses also failed to demonstrate embryo or fetal harm (1).
In pregnant sheep, the mean fetal:maternal serum ratio at the end of an infusion of esmolol was 0.08 (2). The drug was not detectable in the fetus 10 minutes after the end of the infusion. However, the hemodynamic effects in the fetal sheep, in terms of decreases in mean arterial pressure and heart rate, were similar to those in the mothers.
A 31-year-old woman at 22 weeks’ gestation complicated by a subarachnoid hemorrhage was treated with esmolol prior to induction of anesthesia (3). The estimated weight of her fetus, by ultrasound, was 350 g. She was administered bolus doses of esmolol of up to 2 mg/kg with a continuous infusion of 200 g/kg/minute. Fetal heart rate (FHR) decreased from 139144 beats/minute to 131137 beats/minute during esmolol treatment. No loss in FHR variability was observed. Administration of the drug was continued during surgery. A healthy, 2880-g boy was delivered at 37 weeks’ gestation who was alive and well at 9 months of age.
A 29-year-old woman at 38 weeks’ gestation presented with supraventricular tachycardia thought to be due to thyrotoxicosis (4). The FHR was 150160 beats/minute. A bolus dose of esmolol, 0.5 mg/kg, followed by a continuous infusion of 50 g/kg/minute was given to the mother. Approximately 20 minutes later, the FHR increased to 170175 beats/minute, then 4 minutes later fell to 7080 beats/minute. The severe bradycardia persisted despite stopping the esmolol, and an emergency cesarean section was performed to deliver a 2660-g male infant. The infant’s initial pulse was 60 beats/minute, but increased to 140 beats/minute within 60 seconds in response to oxygen therapy. The umbilical vein blood pH was 7.09. The mother’s arrhythmia was successfully converted after delivery with verapamil. Both mother and infant recovered uneventfully. The authors speculated that the cause of the fetal bradycardia was an esmolol-induced decrease in placental blood flow or interference with fetal compensation for a marginal placental perfusion (4).
A laboring mother at 39 weeks’ gestation had a recurrence of tachyarrhythmia (225235 beats/minute) that resulted in symptomatic hypotension and fetal bradycardia (5). She was treated with esmolol by IV bolus and continuous infusion (total dose 1060 mg) until delivery of 3390-g female infant with Apgar scores of 7 and 9. Symptoms of b-blockade in the infant included hypotonicity, weak cry, and dusky appearance and apnea with feeding, but except for mild jaundice, other evaluations (calcium, magnesium, and glucose serum levels) were normal. The feeding difficulties had resolved by 48 hours of age and the other symptoms by 60 hours of age.
In another case, b-blockade in the fetus and newborn were described in a case in which the mother was treated with esmolol, 25 g/kg/minute, for hypertrophic obstructive cardiomyopathy during labor (6). Within 10 minutes of starting esmolol and receiving IV fentanyl, the fetal heart declined from 160 beats/minute to 100 beats/minute with loss of beat-to-beat variability. The newborn had Apgar scores of 8 and 9 at 1 and 5 minutes, respectively, but was hypotensive (mean arterial pressure 3439 mmHg), mildly hypotonic, hypoglycemic, and fed poorly. All of the symptoms had resolved by 36 hours of age.
A 1994 report described a woman who suffered a myocardial infarction at 26 weeks’ gestation who was treated with an infusion of esmolol and other agents (7). She eventually delivered a healthy female infant at 39 weeks.
Breast Feeding Summary
No reports describing the use of esmolol during lactation have been located. Because of the indications for this drug and the fact that it must be given by injection, the opportunities for use of esmolol while nursing are probably nil.
- Product information. Brevibloc. Baxter Pharmaceutical, 2000.
- Ostman PL, Chestnut DH, Robillard JE, Weiner CP, Hdez MJ. Transplacental passage and hemodynamic effects of esmolol in the gravid ewe. Anesthesiology 1988;69:73841.
- Losasso TJ, Muzzi DA, Cucchiara RF. Response of fetal heart rate to maternal administration of esmolol. Anesthesiology 1991;74:7824.
- Ducey JP, Knape KG. Maternal esmolol administration resulting in fetal distress and cesarean section in a term pregnancy. Anesthesiology 1992;77:82932.
- Gilson GJ, Knieriem KJ, Smith JF, Izquierdo L, Chatterjee MS, Curet LB. Short-acting beta-adrenergic blockade and the fetus. A case report. J Reprod Med 1992;37:2779.
- Fairley CJ, Clarke JT. Use of esmolol in a parturient with hypertrophic obstructive cardiomyopathy. Br J Anaesthesia 1995;75:8014.
- Sanchez-Ramos L, Chami YG, Bass TA, DelValle GO, Adair CD. Myocardial infarction during pregnancy: management with transluminal coronary angioplasty and metallic intracoronary stents. Am J Obstet Gynecol 1994;171:13923.