Obstetrics | Tocolytics

Hi everyone, welcome back to the MedBullets Step 2 in 3 podcast. In today's episode, we cover the topic of togolytics found under the obstetrics section at MedBullets.com. Let's begin with a clinical snapshot. A 24-year-old G1P0 presents to a local emergency room with contractions. She is currently 30 weeks pregnant. She reports her membranes have not ruptured.

She is given a tocolytic to suppress the contractions. She is also given betamethasone to promote fetal lung maturity. She is transferred to a larger tertiary care center. Let's continue with an introduction to tocolytics. As a reminder, tocolytics are medications that cause uterine relaxation. They may include terbutylene, nifedipine, and endomethacin.

The mechanism of action for terbutylene is that it acts as a beta-2 agonist. For nifedipine, it acts as a calcium channel blocker. And for endomethacin, it is a non-steroidal anti-inflammatory drug. Clinically, they are used to decrease contraction frequency in patients with preterm labor, and it allows time for steroid administration to optimize fetal lung maturity. Adverse effects for terbutylene include restlessness and tachycardia.

Adverse effects of nifedipine include peripheral edema and flushing and dizziness. And for indomethacin, it may cause gastric ulcers and nephrotoxicity. Now that we've discussed the major points relating to tocolytics,

Let's walk through a question to apply what we've learned and get a sense of how the topic might be tested. For this question, consider the following clinical scenario. presents to the L&D triage unit at 33 weeks of gestation with painful uterine contractions. The contractions started 2 hours ago and have been occurring at 5-10 minute intervals. She has not noticed any bleeding.

She has received appropriate prenatal care during the pregnancy. The patient has a past medical history of well-controlled hypertension, thyroid disease, and asthma. Her previous gynecologic history is notable for a loop electrical excision procedure. for cervical intraepithelial neoplasia type 2, noted on routine screening three years ago. Her medications include labetalol, levothyroxine, and as-needed albuterol. She does not use alcohol, tobacco, or other drugs.

Her temperature is 98.6 degrees Fahrenheit or 37.0 degrees Celsius. Blood pressure is 135 over 60. Pulse is 90 beats per minute. Respirations are 22 breaths per minute. and oxygen saturation is 99% on room air. Physical exam demonstrates a firm uterus and a fundal height appropriate for gestational age. Previous transvaginal ultrasound demonstrated no evidence of placenta previa.

Speculum exam demonstrates a cervix dilated to 4 centimeters, intact membranes, and no blood. Fetal Doppler ultrasonography reveals a fetal heart rate of 140 beats per minute, with moderate variability and no decelerations. Which of the following is a side effect of the most appropriate medication for this patient? And the answer choices are, choice 1, constriction of the ductus arteriosus. Choice 2, hypokalemia and pulmonary edema.

Choice three, increased risk of maternal infection and gestational diabetes. Choice four, loss of deep tendon reflexes. Or choice five, tachycardia, hypotension, flushing, and headache. The best answer to this question is choice five, tachycardia, hypotension, flushing, and headache. This patient with painful uterine contractions every five to 10 minutes with a dilated cervix most likely is in preterm labor.

Since this patient is between 32 and 34 weeks of gestation, she should receive short-term therapy with tocolytic nifedipine, which can cause the side effects of tachycardia, hypotension, flushing, and headache. Pre-term labor can significantly increase the risk of adverse fetal outcomes. Administration of tocolytic agents that can delay pre-term labor in the short term is indicated in patients before 34 weeks of gestation.

This allows for administration of antenatal corticosteroids, magnesium sulfate for neuroprotection, and a safe transport of the mother to a tertiary care facility. For patients at less than 32 weeks of gestation, Indomethacin, a non-steroidal anti-inflammatory drug, is the preferred tocolytic. In patients between 32 and 34 weeks of gestation, the calcium channel blocker nifedipine is first-line therapy.

This medication also causes peripheral vasodilation, which leads to side effects of nausea, flushing, headache, dizziness, and palpitations. There are no known significant fetal side effects of nifedipine.

Let's also discuss why the other choices are incorrect. Choice 1. Constriction of the ductus arteriosus is a side effect associated with endomethacin, a tocolytic and NSAID. Indomethacin is therefore not recommended as a tocolytic after 32 weeks of gestation. Fetal echocardiographic evaluation should be performed in patients that are less than 32 weeks of gestation and receive indomethacin for more than 48 hours for tocolysis.

Endomethacin is used to treat patent ductus arteriosus. Choice two, hypokalemia and pulmonary edema are both side effects of terbutylene, a beta-2 agonist and tocolytic. Beta-2 agonists are not recommended as first-line therapies for tocolysis, as they are less effective than calcium channel blockers at prolonging pregnancy. There is a black box warning for terbutylene use longer than 48 to 72 hours for tocolysis.

due to an increased risk of serious fetal and maternal adverse effects, such as arrhythmias, pulmonary edema, myocardial ischemia, and death. Choice three, increased risk of maternal infection and gestational diabetes. are side effects of progesterone. Progesterone may help to prevent preterm labor in patients with short cervix or previous spontaneous preterm birth. However, progesterone is not ineffective tocolytic in patients who have threatened or established preterm labor.

Choice four, loss of deep tendon reflexes is a side effect of magnesium sulfate, a tocolytic of unclear efficacy. Magnesium sulfate can be administered for fetal neuroprotective effects. Maternal side effects of magnesium sulfate therapy also include diaphoresis and flushing. Because this patient is at 33 weeks of gestation, magnesium sulfate administration is not indicated. Finally, a bullet summary.

Nifedipine is the preferred tocolytic agent for women between 32 to 34 weeks of gestation. Side effects of nifedipine include flushing, headache, tachycardia, and hypotension. That's all for this review about Togolitics. We hope that was helpful. This is the MedBullets Step 2 in 3 podcast, a daily audio review session for MedBullets, the free learning and collaboration community.

for medical student education. As a reminder, you can follow along with these podcast episodes by reviewing the topics directly on MedBullets.com. You can listen to these episodes on the MedBullets website or phone app. while reading through the topic. If the MetBullets podcast has been valuable to you, we'd be thrilled if you considered leaving us a 5-star rating and writing us a review on Apple Podcasts. It will help us spread the word.

and increase our discoverability tremendously. Thanks for tuning in. We'll see you all tomorrow, right here, on the MedBullet Step 2 in 3 podcast.