Therapeutic indications
Induction of labour formedical reasons; stimulation of labour in hypotonic uterine inertia;treatment and prevention of postpartum uterine atony and haemorrhage;during caesarean section and delivery of placenta; induction oftherapeutic abortion.
Posology and method of administration
Anoxytocin challenge test should be used to evaluate foetal distress inpregnant patients at high risk. The oxytocin challenge test is designedto detect the foetal and placental states, as well as possiblecomplications during labour.
Intravenous infusion is performed asfollows: oxytocin is diluted in 500 ml of sterile 5 % glucose or 0,9 %sodium chloride. In accordance with British National Formulary Nr. 42guidance oxytocin for induction of labour should be used in standarddilutions of 10 IU/500 ml (infusing 3 ml/hour delivers 0.001 IU/min)or, for higher doses, 30 IU/500 ml (infusing 1ml/hour delivers 0.001IU/min).
For the stimulation of labour in hypotonic uterine inertia or induction of labouroxytocin may be given by slow intravenous drip infusion preferably bymeans of an infusion pump to allow precise adjustment of the flow rate.
Infusion is begun at a rate of 0.001 – 0.002 IU/min and thengradually increased at intervals of at least 30 min, until a maximum of3 or 4 contractions are occurring every 10 min. Foetal heart rate anduterine motility essential for dose titration (never give intravenousbolus injection during labour) should be monitored; infusion should bediscontinued immediately in uterine hyperactivity or foetal distress.
Arate of up to 0.006 IU/min is reported to produce plasma oxytocinconcentrations comparable to those in natural labour, and 0.012 IU/minis usually the most that is needed, but doses of up to 0.02 IU/min ormore may be required.
In accordance with British NationalFormulary Nr. 42 guidance the maximum recommended rate is 0.032 IU/minand maximal total dose not more than 5 IU in any one day. Once labouris progressing, oxytocin infusion may be gradually withdraw.
In the case of caesarean section oxytocin may be given by slow intravenous injection immediately after delivery of placenta in dose to 5 IU.
For the prevention of postpartum haemorrhage, after delivery of placenta oxytocin should be given by slow intravenous injection in dose to 5 IU, for treatment of postpartum haemorrhage -in dose to 5-10 IU, followed in severe cases by intravenous infusion of5-30 IU at a rate sufficient to control uterine atony. Rapidintravenous injection may cause short-lasting drop in blood pressure.Prolonged administration is not recommended (see Special warning andspecial precautions for use).
In abortion for medical reasons5 IU by slow intravenous injection is recommended, followed ifnecessary by intravenous infusion at a rate of 0.02 to 0.04 IU/min orhigher.
Contraindications
Hypersensitivity to oxytocin or any of the components.
Hypertonic uterine contractions, mechanical obstruction to delivery, foetal distress (foetal hypoxia).
Disproportionbetween foetus dimensions and pelvic sizes; transversal or obliqueposition, placenta praevia, vasa praevia, placental abruption, cordpresentation or prolapse, predisposition to uterine rupture as inmultiple pregnancy, polyhydramnios, grand multiparity and presence ofuterine scar from major surgery , including caesarean section.
It isnecessary to avoid prolonged administration in oxytocin–resistantuterine inertia, severe preeclamptic toxaemia or severe cardiovasculardisease.
Special warning and special precautions for use
Oxytocin,when given for induction or enhancement of labour, must be administeredonly by intravenous infusion (drip method) and under adequate medicalsupervision in a hospital. Accurate control of the flow rate isrequired. Besides careful monitoring of uterine motility (frequency,strength, and duration of contractions), foetal heart rate, foetusposition, mother's blood pressure and individual response. Specialprecautions needed:
in presence of borderline cephalopelvic disproportion (avoid if significant),
secondary uterine inertia,
mild or moderate pregnancy-induced hypertension or cardiac disease;
women over 35 years ;
women with history of lower-uterine segment caesarean section;
if foetal death in utero is observed or in presence of meconium –stained amniotic fluid (may cause amniotic fluid embolism).
Becauseoxytocin possesses slight antidiuretic activity, its prolongedintravenous administration at high doses in conjunction with largevolumes of fluid may cause water intoxication associated withhyponatraemia.
To avoid this rare complication anelectrolyte-containing diluent must be used (not glucose); the volumeof infused fluid should be kept low, fluid intake by moth must berestricted; a fluid balance chart should be kept, and serumelectrolytes should be measured when electrolyte imbalance is suspected.
Therapeuticeffects enhanced by concomitant prostaglandins (very careful monitoringis necessary), caudal block anaesthesia (may enhance effects ofsympathomimetic vasopressors) (see section Interaction with othermedicinal products and other forms of interaction).
Interaction with other medicinal products and other forms of interaction
Prostaglandins may potentiate the uterotonic effect of oxytocin and vice versa.
Oxytocin should not be used rather than 6 hours after vaginal administration of prostaglandins.
Someinhalation anaesthetics (e.g. cyclopropane, halothane) may enhance thehypotensive effect of oxytocin and reduce its oxytocic action. Theirconcurrent use with oxitocin has also been reported to cause cardiacrhythm disturbances.
Concomitant administration of oxytocin and vasoconstrictor sympathomimetics may enhance vasopressor effect.
Whengiven during or after caudal block anaesthesia, oxytocin may potentiatethe pressor effect sympathomimetic vasoconstrictor agents.
Pregnancy and lactation
See section Therapeutic indications.
The induction of labour by means of oxytocin should be attempted only when strictly indicated for medical reasons.
Only minimal amounts pass into breast milk. Problems in humans have not been documented.
Effects on ability to drive and use machines
Not applicable.
Undesirable effects
Uterine spasm (may occur at low doses).
Administrationof oxytocin in high doses or to those hypersensitive to it may causeuterine hypertonicity, tetanic contractions, uterine hyperactivitysoft-tissue damage or uterine rupture, foetal bradycardia, foetalarrhythmias, and foetal asphyxiation and acute hypoxia, and perhapsfoetal or maternal death.
Large infusion volumes ofelectrolyte–free fluid may cause water intoxication with pulmonaryoedema, convulsions, coma, hyponatraemia, and even death.
Oxytocinmay occasionally cause nausea, vomiting, cardiac arrithmias; in a fewcases, skin rashes and anaphylactic reactions (with dyspnoea,hypotension or shock) may occur.
Subarachnoid haemorrhage and maternal death from severe hypertension has occurred.
Postpartum haemorrhage and fatal afibrinogenaemia have been reported but may be due to obstetric complications.
Rapid intravenous injection has produced acute transient hypotension, together with flushing and reflex tachycardia.
There are reports of neonatal jaundice and retinal haemorrhage associated with the use of oxytocin in the management of labour.
Overdose
Antidote is unknown.
Overdosemay lead to placental abruption, amniotic fluid embolism, uterinehyperactivity, hypertonicity and tetanic contractions result in uterinerupture, cervical and vaginal lacerations, severe postpartumhaemorrhage, foetal cardiac arrhythmias, hypoxia and even death.
Some effects associated with antidiuretic activity can occur.
Inthe case of overdose infusion should be discontinued immediately,normal diuresis should be maintain, symptomatic therapy is required,electrolyte – containing hypertonic fluid should be used.
