Drugs Acting on Uterus: Stimulants and Relaxants in Action

 Drugs Acting on Uterus: Stimulants and Relaxants in Action

Introduction: The Uterus as a Performer

• Sometimes it needs to beat fast (labor/contraction → stimulants)
• Other times it needs to stay silent (relax during premature labor → relaxants)

Memory Tip (Mnemonic):
"Stimulate to Deliver, Relax to Delay"

Uterine Stimulants (Ecbolics) Overview

• Oxytocin
• Ergometrine
• Misoprostol

Oxytocin – “The Love Hormone Turned Labor Trigger”

Mechanism:

• Acts on oxytocin receptors on myometrium
• ↑ intracellular Ca²⁺ → muscle contraction

Uses:

• Induce/augment labor
• Control postpartum hemorrhage (PPH)
• Milk let-down

Adverse Effects:

• Uterine rupture
• Water intoxication (ADH-like effect)

Memory Tip:
 "Oxytocin opens the gate of love and labor"

Ergometrine – “The Ergot Squeeze”

Mechanism:

• α-adrenergic agonist → ↑ uterine tone
• Direct smooth muscle contraction

Uses:

• Postpartum hemorrhage (PPH)

Adverse Effects:

• Hypertension
• Vasospasm

Memory Tip:
"Ergometrine = Emergency clamp on bleeding"

 Misoprostol – “The Prostaglandin Flame”

Mechanism:

• PGE1 analogue → stimulates uterine contractions & cervical ripening

Uses:

• Medical abortion
• Induce labor
• PPH control

Adverse Effects:

• Diarrhea, abdominal cramps
• Uterine rupture (rare)

Memory Tip:
"Misoprostol: PGE1 = Push Goes Early!"

Uterine Relaxants (Tocolytics) Overview

• Isoxsuprine
• Salbutamol
• Magnesium sulfate
• Nifedipine
• Progesterone

Isoxsuprine – “Smooth Talker to the Uterus”

Mechanism:

• β₂-agonist → relaxes uterine smooth muscle

Uses:

• Delay premature labor

Adverse Effects:

• Tachycardia
• Hypotension

Memory Tip:
💨 "Isox-SUPRINE = Supine Uterus" (relaxed)

Salbutamol – “The Broncho-Uterine Relaxer”

Mechanism:

• β₂-agonist → relaxes uterine muscle (like in asthma)

Uses:

• Preterm labor suppression

Adverse Effects:

• Palpitations
• Tremors
• Pulmonary edema

Memory Tip:
"Salbutamol slows the uterus sprint"

Magnesium Sulfate – “The Muscle Mellowing Mineral”

Mechanism:

• Competes with Ca²⁺ → ↓ uterine contractions
• CNS depressant

Uses:

• Tocolytic
• Prevent seizures in eclampsia

Adverse Effects:

• Respiratory depression
• Hyporeflexia

Memory Tip:
 "MAG = Makes All Go-slow"

 

Nifedipine – “Smooth Operator”

Mechanism:

• Ca²⁺ channel blocker → prevents muscle contraction

Uses:

• Delay labor
• Hypertension in pregnancy

Adverse Effects:

• Flushing
• Headache
• Hypotension

Memory Tip:
"Nife-locks the calcium" = Nifedipine blocks contraction

 

Progesterone – “The Pregnancy Protector”

Mechanism:

• Maintains uterine quiescence
• ↓ prostaglandin production

Uses:

• Prevent preterm labor
• Maintain early pregnancy

Adverse Effects:

• Nausea, drowsiness

Memory Tip:
"PRO-Gestation hormone" = PROgesterone

                                                            END OF THE CHAPTER

You may like to read more:

1. Antimicrobials Made Simple: Mechanism, Resistance, and Smart Usage

2. Classification of Cephalosporins, Monobactams, and Carbapenems

3. Chapters in Pharmacology