What are the drugs that promote uterine contraction?

Giving birth is a very difficult thing in itself, especially for some female friends who are not in good physical condition. They can use some auxiliary methods to make the delivery smoother. The drugs often used to induce labor in clinical practice are drugs that promote uterine contraction. So, what are the drugs that can promote uterine contraction?

Uterotonics are a class of drugs that can selectively excite uterine smooth muscle and cause uterine contractions. Due to different drugs, different dosages and different physiological states of the uterus, the uterus may experience rhythmic or tonic contractions after taking the medicine. Drugs that cause rhythmic contractions of the uterus can be used for inducing labor and accelerating labor before delivery; drugs that cause tonic contractions of the uterus are mostly used for postpartum hemostasis or postpartum uterine recovery. In addition, some drugs are also used for abortion.

Commonly used drugs in clinical practice:

1. Pituitary hormones

(1) Oxytocin

This product is extracted from the neurohypophysis (posterior pituitary) of pigs, cattle and sheep, and can also be artificially synthesized. Their potency is expressed in units, with 1 unit equivalent to 2 µg of pure oxytocin.

Process in the body: It is well absorbed after intramuscular injection, with onset of action within 3-5 minutes and duration of action for 20-30 minutes. Can be absorbed through the nasal cavity. Most of it is destroyed by the liver, and a small part is excreted unchanged in the urine.

Pharmacological action: It has been proven that there are oxytocin receptors in uterine smooth muscle and mammary gland. Oxytocin causes uterine contraction and promotes milk ejection by binding to the receptors. The receptor density in the non-pregnant uterus is low, while the number of receptors in the pregnant uterus gradually increases, reaching its peak in the late pregnancy, and the number of receptors in the uterine body is significantly higher than that in the cervix.

① Excite the uterus: Oxytocin selectively excites the uterine smooth muscle, enhancing uterine contraction. The features are as follows:

The effect is fast and short-lived;

It has a strong stimulating effect on the uterine body and a weak stimulating effect on the cervix;

The nature and intensity of uterine contraction depends on the dose. A small dose causes rhythmic contraction of the uterus, which is similar to normal labor and is beneficial to the delivery of the fetus. A large dose causes tonic contraction of the uterus, which is detrimental to the fetus and mother during labor.

The effect is affected by the physiological state of the uterus: the level of progesterone in the body is high in early pregnancy, which can reduce the sensitivity of the uterus to oxytocin, so the early uterus is insensitive to oxytocin; the sensitivity of the uterus to oxytocin gradually increases in the middle and late pregnancy, reaching a peak at delivery. This is because the estrogen level in the body gradually increases with the progress of pregnancy, and estrogen can increase the sensitivity of the uterus to oxytocin; after delivery, the sensitivity of the uterus to oxytocin gradually decreases.

② Promote milk secretion: Oxytocin can cause the myoepithelial cells around the mammary alveoli to contract, which can promote milk secretion but does not increase the total amount of milk secretion.

③Other effects: Large doses of oxytocin can relax vascular smooth muscle and have a short-term antihypertensive effect; it also has a mild antidiuretic effect.

Clinical Uses:

① Oxygenation and induction of labor:

For dystocia with weak uterine contractions and normal fetal position and birth canal, a small dose of oxytocin can be used to induce labor in order to strengthen the rhythmic contraction of the uterus and promote delivery.

For those who need to terminate the pregnancy early due to stillbirth, overdue pregnancy, or pregnancy complicated by serious diseases (such as heart disease, tuberculosis, etc.), small doses of oxytocin can be used to induce labor.

② Postpartum hemostasis: In case of postpartum hemorrhage, a large dose of oxytocin (5-10 units) should be injected intramuscularly or subcutaneously immediately to cause tonic contraction of the uterus, compressing the blood vessels in the muscle layer and stopping bleeding. However, due to its short-lived effect, it has been replaced clinically by ergonovine, which has a fast and long-lasting effect after intramuscular injection.

③Induce lactation: 2-3 minutes before feeding, apply nasal drops into the nose, 3 drops each time. After being absorbed by the mucous membrane, it can promote milk discharge. 2-5 units of lactation can also be injected intramuscularly.

Adverse reactions:

① Occasionally nausea, vomiting, and arrhythmia;

② Excessive use can lead to persistent tonic contraction of the uterus, causing fetal intrauterine asphyxia or even uterine rupture.

Precautions for use: When oxytocin is used to induce labor or labor, the following points must be noted:

① Strictly control the dosage: adjust the intravenous drip rate in time according to the uterine contraction and fetal heart rate to avoid uterine tonic contraction.

② Strictly observe contraindications: It is forbidden for women with abnormal birth canal, malposition of fetus, cephalopelvic disproportion, placenta previa, women with more than three children, and women with a history of cesarean section to prevent uterine rupture or fetal intrauterine asphyxia.

③ Oxytocin preparations extracted from animal pituitary glands occasionally cause allergic reactions, while artificially synthesized ones do not.

(2) Pituitrin

This product is a crude preparation extracted from the neurohypophysis of pigs, cattle, sheep and other animals, containing equal amounts of oxytocin and vasopressin (antidiuretic hormone).

Oxytocin in posterior pituitary hormone has the effects of stimulating labor, inducing labor or stopping bleeding after delivery. Due to its complex composition, including vasopressin, it is not very selective for uterine smooth muscle and has many adverse reactions. Therefore, it has been replaced by oxytocin as a uterine contraction drug. The vasopressin contained in posterior pituitary hormone has two effects: 1. By binding to the corresponding receptors on the renal collecting ducts, it increases the reabsorption of water and has a significant antidiuretic effect, which can be used to treat diabetes insipidus; 2. It acts on vascular smooth muscle, constricts blood vessels, especially capillaries and visceral arterioles, and can be used to treat pulmonary hemorrhage (hemoptysis) and esophageal and gastric fundus varicose vein bleeding (hematemesis).

In addition, vasopressin has a short-term effect of increasing blood pressure and stimulating gastrointestinal smooth muscles. After using posterior pituitary hormone, adverse reactions such as nausea, vomiting, pale complexion, sweating, palpitations, chest tightness, abdominal pain, constipation and allergic reactions may occur. In such cases, the drug should be stopped immediately. It is contraindicated for patients with hypertension, coronary heart disease, cor pulmonale, heart failure, pregnancy-induced hypertension syndrome, etc. For other contraindications, see oxytocin.