Uterine Stimulants & Relaxants

UTERINE STIMULANTS & RELAXANTS


UTERINE STIMULANTS & RELAXANTS

I) UTERINE STIMULANTS

  • Are drugs increasing uterine contractions.
  • Also known as oxytocics/ecbolics.

Substances causing uterine stimulation:

1. Oxytocin:

  • Secreted by posterior pituitary, along with ADH.

Functions:

  • Increases uterine contractions with complete relaxation on intervals.
  • Increases contraction of upper segment of uterus (fundus & body)
  • Lower segment is relaxed, facilitating fetus expulsion.
  • Uterus sensitivity to oxytocin is increased by Estrogen & decreased by progesterone.
  • Involved in milk ejection reflex (Note: Prolactin causes milk secretion).
  • High oxytocin doses causes fall in BP – Due to vasodilation, resulting in reflex tachycardia.
  • Oxytocin has ADH-like-action in high dose –> Result in fluid retention & water intoxication.

Uses:

  • Labor induction in post-maturity & uterine inertia.
  • Treatment of postpartum hemorrhage (Note: Methylergometrine preferred).
  • Oxytocin challenge test: To know adequacy of uteroplacental circulation in high-risk pregnancies.

Contraindication:

  • Contracted pelvis cases.
  • Injudicious use results in uterus rupture – Due to powerful uterine contractions.
  • Obstructed labor
  • Malpresentation
  • History of LSCS
  • Hypovolemic states
  • Cardiac conditions.

2. Ergot Derivatives

  • Ergometrine derived from Claviceps purpura.
  • Used as an oxytocic agent.
  • Methylergometrine, its derivative – More potent oxytocic.
  • Actions:
    • Produces uterine contractions in upper & lower segment.
    • Used to control postpartum hemorrhage. (Methylergometrine – Preferred)
    • Administered at delivery of anterior shoulder.
    • Preferred over oxytocin for this indication.
  • Contraindications: Hypertension & sepsis.

3. Prostaglandins:

  • PGE2 & PGF– Powerful uterine stimulants (contractor).
  • Eg:
  • Dinoprostone (PGE2) intravaginally & Carboprost (PGF) intraamniotic injection – 
    • Used for inducing mid-trimester abortion.
  • Misoprostol (PGE) along with methotrexate/mifepristone – 
    • Used for abortion induction in 1st few weeks of pregnancy.

II) UTERINE RELAXANTS:

  • Drugs decreasing uterine contractions.
  • Also known as “tocolytics”.

Uses:

  • Mainly to delay labor, on premature contractions.

Drugs:

1. β-agonists:

  • Selective β-agonists.
  • Eg: Ritodrine, isoxsuprine & terbutaline
  • Contraindications:
    • Should not be used in mothers with diabetic/cardiac conditions.
    • Pulmonary edema – Serious complication at high doses.
    • β2-agonists – Causes tachycardia, palpitations, tremors, hyperglycemia & hypokalemia.

2. Magnesium sulfate:

  • Mainly used to control convulsions in eclampsia.
  • Possesses tocolytic activity.
  • Magnesium sulfate by i.v. or inhalational routeTreatment of acute severe asthma.
  • Preferred over β2-agonists in cardiac, diabetic, hypothyroid & hypertensive patients.
  • Toxicity:
    • Initial manifestation: Loss of patellar reflex –> respiratory depression –> finally, cardiac arrhythmias & arrest.

III) Other drugs:

1. Calcium channel blockers:

  • Nifedipine & oxytocin antagonist ‘atosiban’ – Delays premature labor.
  • Provides best balance of successful delayed delivery with lesser risk to mother & baby.

2. Ethyl alcohol (i.v. infusion), NSAIDs & progesterone:

  • Suppresses uterine contractions (used rarely).

3. Halothane:

  • Efficacious tocolytic agent. 
  • Anaesthetic of choice for version (external or internal).

4. Hydroxyprogesterone:

  • Prophylactically prevents pre-term labour.
  • Teratogenic potential limits its use. 

Exam Important

UTERINE STIMULANTS & RELAXANTS

  • Uterine stimulants are also known as oxytocics/ecbolics.
  • Substances causing uterine stimulation include oxytocin, ergot derivatives, prostaglandins (particularly PGE2 & PGF).

Functions of oxytocin as uterine stimulants:

  • Oxytocin increases uterine contractions, increases contraction of upper segment of uterus, relaxes lower segment facilitating fetus expulsion.
  • Oxytocin is mainly used for labor induction in post-maturity & uterine inertia & for postpartum hemorrhage treatment.
  • Methylergometrine, an ergometrine derivative, is a most potent oxytocic substance.
  • Ergometrine derived from Claviceps purpura.
  • PGE2 & PGF– Powerful uterine stimulants.
  • Dinoprostone (PGE2) intravaginally & Carboprost (PGF) intraamniotic injection is used for inducing mid-trimester abortion.
  • Misoprostol (PGE) along with methotrexate/mifepristone is used for abortion induction in 1st few weeks of pregnancy.
  • Uterine relaxants are also known as “tocolytics”.
  • Uterine relaxants are mainly to delay labor, on premature contractions.
  • Uterine relaxants include β-agonists (Ritodrine, isoxsuprine & terbutaline), Magnesium sulfate, calcium channel blockers (Nifedipine & oxytocin antagonist ‘atosiban’), ethyl alcohol (i.v. infusion), NSAIDs, progesterone, Halothane & Hydroxyprogesterone.
  • Magnesium sulfate is used to control convulsions in eclampsia.
  • Magnesium sulfate possesses tocolytic activity.
  • Magnesium sulfate by i.v. or inhalational route is used for treatment of acute severe asthma.
  • Nifedipine & oxytocin antagonist ‘atosiban’ used for delaying premature labor & also provide best balance of successful delayed delivery with lesser risk to mother & baby.
  • Halothane is an efficacious tocolytic agent. 
  • Hydroxyprogesterone prophylactically prevents pre-term labor.

 

Don’t Forget to Solve all the previous Year Question asked on UTERINE STIMULANTS & RELAXANTS

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