Obstetric Pharmacology — Uterotonics & Tocolytics

Oxytotic
(used to augment labour and ↑ uterine tone)

• Oxytocin derivatives (syntocinon, carbitocin)
  • Oxytocin synthesised in hypothalamus
  • Gq-PCR on SM cells
  • causing increased Ca influx
  • Ca induced Ca relase from SR → SM contraction
    • Cause milk ejection from mamary glands, hypotension (via relaxation of SM), arrhythmias, water retention (similar structure to ADH)
• Ergot derivatives (ergometrine)
  • Acts on alpha 1 and 5HT2 recepters (both Gq-PCRs) on uterine and vascular SM cells
  • ↑ force and freq of contractions
  • ↑ uterine tone
  • contraction of cervix.
• Prostaglandins
  • PGF2 alpha (Gq-PCR)
  • Intra myometrial injection
  • causes ↑ SM tone
  • Bronchospasm if injected intravenously.

Tocolytic
(↓ uterine tone to suppress pre-term labour)

• Beta 2 agonists (salbutamol)
  • β2 receptors action → ↑AC → ↑ cAMP → ↑PLC → ↓calcium → relaxation of myometrial SMCs
  • Tachycardia/tremour/hypokalaemia
• Ca-channel blockers (nifedipine)
  • ↓d Ca influx due to action on l-type Ca channels → ↓ uterine tone
  •  Inhibition of hypoxic pulmonary vasoconstriction, Impaired platlet aggregation, Headache, flushing and dizziness, Peripheral oedema
• NSAIDs (indomethacin)
  • ↓ formation of PGE2 and PGF2α → ↓ uterine tone
  • Can cause premature closure of ductus arteriosus, oligohydramnios, NEC and broncho-pulmonary dysplasia

Gladwin 2016

Click here for CICMWrecks Pharmacopeia Table for Oxytocics and Tocolytics

Answer by Gladwin