How oxytocin works
The hormone oxytocin is produced in the hypothalamus (section of the diencephalon) and released by the pituitary gland (hypophysis). It acts both in the brain and in the rest of the body, where it reaches via the blood system.
According to scientific studies, oxytocin causes sexual arousal, bonding behavior and (after birth) maternal care for the newborn in the brain. For this reason, it is often referred to as the “love hormone”.
When released into the bloodstream, oxytocin has a number of effects that are often associated with childbirth. It triggers contractions of the uterine muscles – also known as “contractions” during childbirth. The hormone can therefore be administered externally as a drug to induce an overdue birth or to strengthen contractions that are too weak.
After the birth, oxytocin prevents increased postpartum bleeding and promotes the detachment of the placenta from the uterus. During breastfeeding, it causes the mammary glands to contract so that the milk is transported towards the nipple (milk ejection reflex).
In addition, oxytocin – especially in high doses – can reduce the amount of urine. However, because the hormone is broken down very quickly, this effect is hardly significant in practice.
This explains why oxytocin is less effective at the beginning of a pregnancy (low amount of estrogen) while the excitability of the oxytocin receptors increases significantly at the end of a pregnancy (placenta produces more estrogens).
Absorption, breakdown and excretion
Due to its structure, oxytocin would be inactivated in the stomach, which is why it is administered intravenously.
The time in which the original amount of hormone is broken down by half and thus inactivated is only a few minutes. The hormone is primarily broken down in the kidneys and liver, and also in the mammary gland during breastfeeding.
Pregnant women also have an oxytocin-degrading enzyme in their blood, oxytocinase.
When is oxytocin used?
Oxytocin is approved for use in pregnant women to induce labor and during labor to strengthen or stimulate contractions. After the birth, the hormone is administered to prevent bleeding (bleeding prophylaxis) and to accelerate the expulsion of the placenta.
In some countries, an oxytocin nasal spray is available on the market which is used to stimulate milk let-down (but not milk production) from the mammary glands.
Outside the officially approved areas of application (i.e. “off-label”), oxytocin is sometimes administered for autism or other behavioral disorders.
Duration of use
How oxytocin is used
Oxytocin is mainly administered as an infusion. Because the active ingredient is inactivated so quickly in the body (especially in pregnant women), continuous administration is necessary to maintain the effect. The oxytocin circulating in the blood does not reach the brain because it cannot cross the blood-brain barrier.
An oxytocin nasal spray is used particularly outside the approved areas of application, as this is more practical than an infusion, especially when used several times a day over longer periods of time. In contrast to an infusion, an oxytocin spray allows some of the hormone to reach the brain.
What are the side effects of oxytocin?
Common side effects that occur in one in ten to one in a hundred patients are excessive contractions, cardiac arrhythmia, heartbeat that is too fast or too slow, increase in blood pressure, headaches, nausea and vomiting.
Occasionally (in every hundredth to thousandth patient) allergic reactions and permanent contractions of the uterus occur.
What should be considered when using oxytocin?
Contraindications
Oxytocin must not be used in the following cases
- Pre-eclampsia (pregnancy-specific disease with, among other things, high blood pressure and water retention in the tissue)
- convulsive labor
- mechanical obstructions to birth
- impending uterine rupture (uterine rupture)
- premature detachment of the placenta
- Acute severe oxygen deficiency of the child
- Positional anomalies of the child
Interactions
As the active substance is a natural hormone, interactions with other drugs are rare. First and foremost, drugs that cause QT prolongation, i.e. a special form of cardiac rhythm change, should be mentioned here.
These include some antidepressants (such as amitriptyline, venlafaxine, sertraline), asthma medications (such as salbutamol, terbutaline), antibiotics (such as erythromycin, ciprofloxacin, azithromycin) and antifungals (such as fluconazole, ketoconazole).
Prostaglandins should not be administered before oxytocin, as otherwise the uterine muscles will react much more strongly to the active substance.
Caution should be exercised with the simultaneous use of medication that affects blood pressure (such as high blood pressure medication).
Age restriction
According to the approval, the area of application only includes pregnant women and women immediately after giving birth. The extent of the benefits and risks of off-label use of the hormone in children and adults with mostly mental illnesses has not yet been sufficiently clarified.
Off-label use is therefore decided on an individual basis by the treating doctor.
Pregnancy and breastfeeding
If oxytocin is used during breastfeeding to promote milk flow, a small amount may pass into breast milk. However, there is no risk of side effects in the infant, as oxytocin is very quickly inactivated in the stomach.
How to obtain medication with oxytocin
Oxytocin is usually administered by a doctor (usually as an infusion).
The oxytocin nasal spray has not been commercially available in Germany as a finished product since 2008, but can be prepared as an individual prescription in pharmacies – but only after a doctor’s prescription.
How long has oxytocin been known?
The hormone oxytocin was discovered at the beginning of the last century. Its effect on the uterus was first described by the British biochemist Henry Hallett Dale in 1906.
The hormone was given its name (from the Greek “okytokos”, meaning easy-bearing) in 1927. The structural composition was not decoded until 1953, which laid the foundation for the production of the active ingredient in relevant quantities.