OXYTOCIN INJECTION 10IU/1ML 10'S

Indications

• Induction of labor
• Management of postpartum hemorrhage
• Facilitation of uterine contraction during labor

Dosage

Children: Dosing information for pediatric use of oxytocin is not provided in the BNF. Consult the BNF for Children for appropriate guidance.

Adults: For induction of labor, oxytocin is typically administered intravenously, starting with a low dose and adjusted based on uterine response. Refer to the BNF for specific dosing guidelines.

Mechanism of action

Oxytocin induces uterine contractions by binding to oxytocin receptors on the myometrium, which are significantly upregulated during pregnancy. This binding triggers a cascade that increases intracellular calcium in uterine myofibrils, leading to enhanced contraction strength and frequency. The hormone's secretion is regulated by a positive feedback mechanism, where the pressure of the fetus against the cervix stimulates further release of oxytocin, thus facilitating labor.

Pharmacodynamics

As a pleiotropic hormone, oxytocin influences numerous physiological processes beyond childbirth, including lactation, metabolism, cardiovascular function, and social behaviors. Its receptors are widely distributed, including in the central nervous system, where they affect emotional and social functions. Oxytocin's action is characterized by its ability to modulate both reproductive and non-reproductive behaviors, suggesting its broad physiological impact.

Pharmacokinetics

Oxytocin is administered either intravenously or intramuscularly, with rapid absorption and onset of action. Its half-life is relatively short, generally around 3 to 5 minutes, necessitating continuous infusion or repeated dosing to maintain effective levels during labor. The distribution volume is extensive, and it is metabolized in the liver and kidneys. Exogenous oxytocin exhibits similar pharmacokinetics to the endogenous form, ensuring effective therapeutic outcomes.

Contra-indications

• Severe fetal distress
• Hypersensitivity to oxytocin
• Uterine hypertonicity
• Certain cardiovascular disorders
• Active genital herpes infection
• Placenta previa

Adverse effects

• Nausea
• Vomiting
• Uterine hypertonicity
• Water retention
• Hypotension
• Tachycardia
• Allergic reactions

Interactions

• Misoprostol may have an additive effect when used with oxytocin

Precautions

• Use with caution in patients with pre-existing cardiovascular conditions
• Monitor for excessive uterine contractions
• Caution in patients with a history of uterine surgery
• Consider the risk of water intoxication with large doses

Pregnancy

Oxytocin is used during pregnancy for induction of labor and to prevent postpartum hemorrhage.

Breast-feeding

Oxytocin is excreted in breast milk, but its effects on a nursing infant are not well established. Monitor for potential effects.

Storage

Store in a refrigerator at 2-8 degrees Celsius. Protect from light and keep out of reach of children.

Formulations

• Injection solution

Mechanism of action

Oxytocin plays a vital role in labour and delivery. The hormone is produced in the hypothalamus and is secreted from the paraventricular nucleus to the posterior pituitary where it is stored. It is then released in pulses during childbirth to induce uterine contractions. The concentration of oxytocin receptors on the myometrium increases significantly during pregnancy and reaches a peak in early labor. Activation of oxytocin receptors on the myometrium triggers a downstream cascade that leads to increased intracellular calcium in uterine myofibrils which strengthens and increases the frequency of uterine contractions. In humans, most hormones are regulated by negative feedback; however, oxytocin is one of the few that is regulated by positive feedback. The head of the fetus pushing on the cervix signals the release of oxytocin from the posterior pituitary of the mother. Oxytocin then travels to the uterus where it stimulates uterine contractions. The elicited uterine contractions will then stimulate the release of increasing amounts of oxytocin. This positive feedback loop will continue until parturition. Since exogenously administered and endogenously secreted oxytocin result in the same effects on the female reproductive system, synthetic oxytocin may be used in specific instances during the antepartum and postpartum period to induce or improve uterine contractions. The pharmacologic and clinical properties of oxytocin are identical with those of naturally occurring oxytocin principle of the posterior lobe of pituitary. Oxytocin exerts a selective action on the smooth musculature of the uterus, particularly toward the end of pregnancy, during labor, and immediately following delivery. Oxytocin stimulates rhythmic contractions of the uterus, increases the frequency of existing contractions, and raises the tone of the uterine musculature. Oxytocin indirectly stimulates contraction of uterine smooth muscle by increasing the sodium permeability of uterine myofibrils. High estrogen concentrations lower the threshold for uterine response to oxytocin. Uterine response to oxytocin increases with the duration of pregnancy and is greater in patients who are in labor than those not in labor; only very large doses elicit contractions in early pregnancy. Contractions produced in the term uterus by oxytocin are similar to those occurring during spontaneous labor. In the term uterus, oxytocin increases the amplitude and frequency of uterine contractions which in turn tend to decrease cervical activity producing dilation and effacement of the cervix and to transiently impede uterine blood flow. Oxytocin contracts myoepithelial cells surrounding the alveoli of the breasts, forcing milk from the alveoli into the larger ducts and thus facilitating milk ejection. The drug possesses no galactopoietic properties. Oxytocin produces vasodilation of vascular smooth muscle, increasing renal, coronary, and cerebral blood flow. Blood pressure is usually unchanged, but following iv administration of very large doses or undiluted solutions, blood pressure may decrease transiently, and tachycardia and an increase in cardiac output may be reflexly induced. Any initial fall in blood pressure is usually followed by a small but sustained increase in blood pressure. In contrast to vasopressin, oxytocin has minimal antidiuretic effects; however, water intoxication may occur when oxytocin is administered with an excessive volume of electrolyte-free iv fluids and/or at too rapid a rate. For more Mechanism of Action (Complete) data for Oxytocin (15 total), please visit the HSDB record page.

Pharmacodynamics

Oxytocin is a nonapeptide, pleiotropic hormone that exerts important physiological effects. It is most well known to stimulate parturition and lactation, but also has important physiological influences on metabolic and cardiovascular functions, sexual and maternal behaviour, pair bonding, social cognition, and fear conditioning. It is worth noting that oxytocin receptors are not limited to the reproductive system but can be found in many peripheral tissues and in central nervous system structures including the brain stem and amygdala.