Oxytocin

Oxytocin is indicated in-

• Induction of labor, stimulation of uterine contractions.
• Post delivery period, for the prevention or treatment of secondary haemorrhage and adherent placenta.
• To stimulate lactation, only it advised by the registered Gynaecologist/Physician.
• Treatment of incomplete abortion to obtain more rapid expulsion in order to prevent secondary hemorrhage.

The active substance of this preparation is synthetically prepared oxytocin, which is identical to the natural occurring hormone from the posterior pituitary gland. Oxytocin causes contractions of the uterus, thus mimicking contractions of normal, spontaneous labor and transiently impeding uterine blood flow. Amplitude and duration of uterine contractions are increased, leading to dilation and effacement of the cervix. Oxytocin also stimulates the smooth muscle associated with the secretory epithelium of the lactating breast causing ejection of milk out of the mammary ductular system but having no direct effect on milk secretion. Oxytocin has only minimal cardiovascular and antidiuretic properties. Therefore, it can safely be administered to patients in whom a (further) increase in blood pressure must be avoided, as in the case of hypertension, toxaemia, (pre-) eclampsia, solutio placentae and uraemia.

Uterine motility depends on the formation of the contractile protein actomyosin under the influence of the Ca²⁺ dependent phosphorylating enzyme myosin light-chain kinase. Oxytocin promotes contractions by increasing the intracellular Ca²⁺, which in turn activates myosin's light chain kinase. Oxytocin has specific receptors in the muscle lining of the uterus and the receptor concentration increases greatly during pregnancy, reaching a maximum in early labor at term.

Induction of labor, stimulation of uterine contractions: Oxytocin should be given by intravenous infusion under adequate control, 1-5 IU added to 500 ml of infusion fluid. The administration is started at 1 mU (1 mU=0.001 IU) per minute. According to the effect obtained the dosage can be doubled every 30-45 minutes until the uterus threshold has been attained. A further increase will then usually provide optimal activity. The threshold is generally below 10 mU per minute.

N.B.: Intramuscular administration of Oxytocin may lead to an irregular response and symptoms of overdosage. It intramuscular administration is nevertheless unavoidable, dosage should not exceed 0.5-1 IU per injection.

Post delivery period, for the prevention or treatment of secondary haemorrhage and adherent placenta: Intramuscular injection of 2-5 IU, or as intravenous infusion in an adequate dosage

To stimulate lactation, only it advised by the registered Gynaecologist/Physician: Intramuscular injection of 2 IU

Treatment of incomplete abortion to obtain more rapid expulsion in order to prevent secondary hemorrhage: Intramuscular injection of 2-5 IU every 30-60 minutes or as intravenous infusion in an adequate dosage

Severe hypertension has been reported when Oxytocin was given three to four hours following prophylactic administration of a vasoconstrictor in conjunction with caudal-block anesthesia. Cyclopropane anesthesia may modify Oxytocin’s cardiovascular effects, so as to produce unexpected results such as hypotension. Maternal sinus bradycardia with abnormal atrioventricular rhythms has also been noted when Oxytocin was used concomitantly with cyclopropane anesthesia.

• Cephalo-pelvic disproportion.
• Abnormal position of the child or abnormal position of the skull.
• Overdistention of the inferior segment of the uterus.
• Severe toxaemia.
• Hypertonic uterine dysfunction.
• Foetal distress, where delivery is not imminent (uterine contractions may increase hypoxia).
• Cord presentation and prolapse.
• Total placenta previa.
• Vasa praevia.

• Hypersensitivity to the drug may result in uterine hypertonicity, spasm, titanic contraction or rupture of the uterus. 
• The possibility of increased blood loss and afbrinigenemia should be kept in mind when administering the drug.
• Severe water intoxication with convulsions and coma has occurred. 
• Oxytocin may occasionally cause nausea, vomiting, haemorrhage or cardiac arrhythmias, anaphylactic reaction.

Adverse reactions: Exceptionally, symptoms of water intoxication may occur. An increased incidence of icterus neonatorum has been reported after use of oxytocin.

Pregnancy category C. It is not known whether Oxytocin is excreted in human milk

• Since uterine sensitivity to oxytocin may vary widely. Oxytocin should be used with care. The smallest effective dose must be determined for each patient and then utilized to initiate labor.
• Oxytocin should only be used when adequate medical supervision is provided. Fetal heart rate and maternal blood pressure should be determined.
• Oxytocin should be used with care if scars of the uterus and of the cervix uteri exist.

Excess oxytocin may cause violent uterine contractions leading to fetal bradycardia and arrhythmias, extensive laceration of the soft tissues, uterine rupture and perhaps fetal or maternal death. Treatment consists of immediate discontinuation of the infusion and induction of tocolysis.

Drugs acting on the Uterus

Oxytocin has been shown not to lose its potency for at least 24 hours (at room temperature and in daylight conditions) when diluted with one of the following infusion fluids:

• Sodium chloride 0.9%
• Anhydrous glucose 5%

With these infusion fluids, Oxytocin can also be injected directly into the infusion line without causing precipitation of the ingredients.

Direct injection into the infusion line is also possible with the following infusion fluids, provided that there are no contra-indications of perfusion of the Individual fluids.

• Sorbitol 5%
• Invert sugar 10%
• Ringer's solution
• Hartmann's solution (Ringer-lactate);
• Rheomacrodex
• Vamin

However, in the later fluids the 24-hours stability has not been established

Store in between 2 to 8°C, in dark & frost free place. Keep out of the reach of children.