Which is an example of a tocolytic agent?

NORCET 2 -2021 (Shift-2)

Pharmacology

Easy

Appeared in: NORCET 2 -2021 (Shift-2)

Explanation

Tocolytic agents are drugs used to suppress or delay preterm labor by inhibiting uterine contractions.
Magnesium sulfate (MgSO4) is a commonly used tocolytic agent that relaxes the smooth muscle of the uterus, thereby decreasing the frequency and intensity of contractions.
Beyond its tocolytic effects, MgSO4 is also critically used for neuroprotection of the fetus in preterm labor and for preventing and treating seizures in patients with preeclampsia and eclampsia.

Option B: Oxytocin is a uterotonic, meaning it stimulates uterine contractions, which is the opposite of a tocolytic's function.
Option C: Ergot derivatives (like methylergonovine) are potent uterotonics that cause sustained uterine contractions.
Option D: Phenergan (promethazine) is an antihistamine with antiemetic and sedative properties. It has no direct effect on uterine contractility.

Visual 1: Flowchart - A flowchart illustrating the mechanism of action of MgSO4 on uterine muscle cells, showing how it competes with calcium to induce muscle relaxation.
Visual 2: Comparison Table - An infographic visually comparing tocolytic agents (e.g., MgSO4, Nifedipine, Terbutaline) with uterotonic agents (e.g., Oxytocin, Methylergonovine, Misoprostol), highlighting their opposing effects and uses.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Pharmacology of Tocolytic and Uterotonic Agents as background academic context rather than a clinical decision trigger.
A primary nursing responsibility during MgSO4 infusion is vigilant monitoring for signs of magnesium toxicity. This includes checking respiratory rate (risk of depression), deep tendon reflexes (loss of reflexes is an early sign), and urinary output (decreased output can lead to accumulation).
The therapeutic range for MgSO4 is narrow, making patient assessment crucial. The antidote, calcium gluconate, must always be readily available at the bedside when a patient is on an MgSO4 infusion.
What if? If a patient on an MgSO4 infusion for preterm labor develops a respiratory rate of 10 breaths/minute and becomes lethargic, the nurse's immediate priority is to stop the infusion, notify the provider, and prepare to administer calcium gluconate.

How to Approach the Question

First, identify the key term in the question: 'tocolytic agent'.
Break down the term: 'Toco-' relates to childbirth/contractions, and '-lytic' means to break down or stop. Therefore, a tocolytic is a drug that stops labor contractions.
Evaluate each option based on this definition.
Recall the primary use of each drug: Oxytocin induces labor, Ergot derivatives are for postpartum bleeding, and Phenergan is for nausea.
Recognize that MgSO4 is widely used in obstetrics to manage preterm labor and preeclampsia, fitting the definition of a tocolytic.
Select MgSO4 as the only option that suppresses uterine contractions.

Concept Tested & Keywords

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