Oxytocin

Section 1.1

Midwives may independently prescribe, order and administer this drug.

Oxytocin is a hormone that simulates uterine smooth muscle to contract by activating protein receptors which act on myofibrils. Oxytocin increases production of prostaglandin which further stimulates uterine contractions.

Indications and Clinical Use:

As a first line agent used intramuscularly or intravenously: 1) for active management to prevent postpartum hemorrhage 2) to treat postpartum hemorrhage due to uterine atony 3) for induction and augmentation of labour (see Oxytocin for Induction of Labour).

Contraindications:

Hypersensitivity to oxytocin or any component of the formulation. For induction and augmentation, any contraindication to labour including: placenta previa, vasa previa, cord presentation, fetal malpresentation such as transverse or footling breech, prior classical or inverted T cesarean section, previous uterine surgery such as myometrial incision, active genital herpes, pelvic structural deformities, cervical carcinoma, previous uterine rupture.

Warnings and Precautions:

A midwife with specialized practice certification may, on her own responsibility, initiate induction of labour in hospital with a cervical ripening agent and/or initiate and manage an IV oxytocin induction/augmentation of labour.

Midwives without specialized practice certification may only administer oxytocin as an IV infusion for induction or augmentation of labour with a physician order.

Oxytocin is structurally and functionally related to vasopressin and its antidiuretic action can lead to water retention. For this reason electrolyte-containing solutions should be used when administering oxytocin. Water intoxication can lead to hyponatremia, confusion, convulsions, coma, congestive heart failure, and death. Fluid overload and hyponatremia with concurrent oxytocin administration may be prevented by strict intake and output recordings, use of balanced salt solutions such as Normal Saline or Lactated Ringers, and avoiding prolonged administration of an infusion of 20 to 40 units of oxytocin.

Oxytocin VIAL STORAGE: Store between 15 and 30˚C. DO NOT FREEZE. (Check specific manufacturer product monograph for most accurate storage conditions.)

Oxytocin Ampoule STORAGE: Store between 2˚C 8˚C. May be stored up to 30˚C for months, but then must be discarded.  Protect from freezing. (Check specific manufacturer product monograph for most accurate storage conditions.)

Pregnancy:

Compatible for induction or augmentation of labour

Lactation:

Category L2 – Limited Data – Probably Compatible

Adverse Reactions:

Arrhythmias, hypertensive episodes, nausea, vomiting, uterine hypertonicity, tetanic contraction of the uterus, uterine spasm, anaphylactic reaction, subarachnoid hemorrhage, severe water intoxication with convulsions, coma, and death is associated with a slow oxytocin infusion over 24 hours.

1) Active Management of the Third Stage of Labour:

Dosage and Administration:

10 Units IM or;
20 Units to 40 Units added to 1000 mL normal saline or ringers lactate and administered IV at a rate of 100-150 mL/hr or;
5 Units IV bolus given slowly over 1-2 minutes;

2) Treatment of postpartum hemorrhage:

Dosage and Administration:

10 units IM and/or;
20 to 40 Units added to 1000 mL of normal saline or ringers lactate and administered at a rate of 250 ml/hr

Onset of Action:

IM: 2-5 minutes
IV: 1-5 minutes

Duration of Action:

IM and IV: 30-50 minutes

Half-life

IM and IV: 6-15 minutes.

*Reference ranges for the onset and duration of action and half-life are varied in the literature.

3) Induction and augmentation of labour:

See section 2.1: Drugs which a midwife may administer after consulting with and on the order of a medical practitioner.

As with any induction method where a physician has prescribed the inducing or augmenting pharmacological agent, the midwife may continue to be involved in care as the condition warrants. A midwife with specialized practice certification may on her own responsibility initiate induction of labour in hospital with a cervical ripening agent and/or initiate and manage an IV oxytocin induction/ augmentation of labour.