Oxytocin

Question 1

What type of medication is oxytocin?

Answer 1

A synthetic oxytocic

Question 2

What is the mechanism of action of oxytocin?

Answer 2

• Oxytocin stimulates receptors in the uterus to cause the muscle fibres to contract.
• When given after the birth, the stimulation causes contractions that aid in shortening the time of the third stage of labour, and also decreases the risk of a postpartum haemorrhage. It does this by using the contractions to detach the placenta from the uterine wall, and the continued contraction of the uterine fibres help to expel any blood or clots in the uterine cavity.
• When given to treat a postpartum haemorrhage its main aim is to increase the amount of contractinos to help with minimising blood loss.

Oxytocin works by increasing the concentration of calcium inside muscle cells that control contraction of the uterus. Increased calcium increases contraction of the uterus.

Question 3

What are the routes of administration, and their onsets, peaks and durations for oxytocin?

Answer 3

• Route: IM
  
  • Onset: 2 - 4 min
  • Peak: N/A
  • Duration: 30 - 60 min
• Route: IV
  
  • Onset: < 1 min
  • Peak: N/A
  • Duration: N/A

Question 4

What are the adverse effects of oxytocin?

Answer 4

• Common: headache, tachycardia, bradycardia, nausea, vomiting.
• Rare: anaphylactoid(1) reaction with dyspnoea, hypotension, shock, rash and arrhythmias.

(1) : Anaphylactoid reactions are reactions that produce the same clinical picture as anaphylaxis, but are not IgE mediated. They occur through a direct nonimmune-mediated release of mediators from mast cells and/or basophils, or result from direct complement activation(2).
(2) : The anaphylactic reaction typically requires antigen-antibody complexes for activation (specific immune response), whereas the alternative (complement activation) pathway can be activated by spontaneous complement component 3 (C3) hydrolysis, foreign material, pathogens, or damaged cells.

Question 5

What are the contraindications of oxytocin?

Answer 5

Allergy or hypersensitivity to oxytocin.

Question 6

What is the preparation and dosage of oxytocin?

Answer 6

• Preparation: 10 IU (1mL) ampoule
• Dosage
  
  • Maternal postpartum care.
    
    • Indication: Prophylaxis post childbirth - Paramedics must ensure that all foetuses have been delivered prior to administration.
    • All ages: Initial dose 10 IU
      
      • Repeat: Nil
      • Max Total Dose: 10 IU
  • Postpartum haemorrhage.
    
    • Dose: IM bolus followed by oxytocin infusion (ALS/ICP only). Infusion preparation: 10IU (1mL) oxytocin diluted to 60mL with 59mL compound sodium lactate via burette with microdrip (1IU:6mL)
      
      • IM: 10 IU
        
        • Repeat: Nil
        • Max Total Dose: 10 IU
      • INF: 60 drops/min (10 IU/hr)
        
        • Repeat: 1
        • Max Total Dose: 20 IU over 2hrs