1) Molecular structure, chemical family, native pathway, receptor & signaling
Item | Oxytocin | Ergometrine (Ergonovine) | PGE1 analog: Misoprostol | PGE2: Dinoprostone | PGF2α analog: Carboprost (± PGF2α dinoprost) | Mifepristone (RU-486) |
Molecular / chemical class | Nonapeptide hormone (9 aa), cyclic (disulfide bridge) | Ergot alkaloid (lysergic acid amide derivative) | Synthetic prostaglandin E1 analog (methyl ester prodrug → active acid) | Natural prostaglandin E2 (or formulated) | Synthetic 15-methyl PGF2α analog (carboprost) / PGF2α (dinoprost) | Synthetic steroid (19-nor steroid) |
Endogenous origin / pathway | Made in hypothalamus (PVN/SON) → released from posterior pituitary; acts as hormone + neuropeptide | Derived from Claviceps ergot; pharmacologic uterotonic | Prostanoids come from arachidonic acid via COX-1/COX-2 → PGH2 → PGE/PGF synthases; misoprostol mimics PGE1 | Same COX pathway; dinoprostone is PGE2 | Same COX pathway; carboprost mimics PGF2α | Not a prostanoid; receptor antagonist steroid |
Primary receptor target | Oxytocin receptor (OXTR) | No single “uterine receptor”; uterotonic effect mainly via 5-HT2 (serotonin) and α1-adrenergic actions on smooth muscle (partial agonist activity) Dopamine R -mild | EP prostaglandin receptors (tissue-dependent: EP2/EP3/EP4 most relevant clinically) | EP receptors (cervix + uterus) | FP receptor (PGF receptor) | Progesterone receptor (PR) competitive antagonist (higher PR affinity than progesterone); also glucocorticoid receptor (GR) antagonist at higher doses |
Second messenger / signaling | Gq/11 → PLC → IP3/DAG → ↑ intracellular Ca²⁺; also ↑ prostaglandin production & gap junctions in myometrium near term | Gq (5-HT2, α1) → PLC/IP3/DAG → ↑ Ca²⁺ → strong contraction + vasoconstriction | Depends on EP subtype: EP3 (Gi ↓cAMP → contraction); EP1 (Gq) contractile; EP2/EP4 (Gs ↑cAMP → relaxation); cervix effects include ECM remodeling | Same EP logic; major clinical effect = cervical ripening + uterine activity | FP is Gq → ↑ Ca²⁺ → strong uterine contraction; bronchial + GI smooth muscle contraction | PR blockade → decidual breakdown, ↑ uterine sensitivity to prostaglandins, cervical softening, and supports uterine contractility indirectly |
Key tissue actions | Uterus (term): rhythmic contractions; breast: milk ejection | Uterus: sustained tetanic contraction (esp. postpartum); vessels: vasoconstriction | Cervical ripening + uterine contractions; also GI smooth muscle | Best “cervix drug”: ripening + uterine contractions | Powerful uterotonic (2nd-line in PPH); broncho constriction risk | Abortifacient priming agent; used with prostaglandin (e.g., misoprostol) for effectiveness |
2) Pharmacokinetics (PK): routes, onset, duration, metabolism, special notes
PK feature | Oxytocin | Ergometrine | Misoprostol (PGE1 analog) | Dinoprostone (PGE2) | Carboprost (PGF2α analog) | Mifepristone |
Common routes (clinical use) | IV infusion (induction/augmentation), IM (PPH) | IM / slow IV (PPH); sometimes oral (limited/variable) | Oral / buccal / sublingual / vaginal / rectal (context-dependent) | Vaginal gel/insert, intracervical; sometimes oral (less common) | IM (and sometimes intramyometrial) for PPH | Oral |
Absorption / activation | Peptide → not oral (GI breakdown) | Well absorbed IM/IV; oral variable | Prodrug rapidly de-esterified to misoprostol acid (active) | Local delivery (vaginal/cervical) gives high local effect | Rapid systemic effect after IM | Well absorbed orally |
Onset / duration (practical) | IV: immediate; IM: minutes; duration short if infusion stopped | IM: minutes; IV: very rapid; longer effect than oxytocin | Oral/sublingual faster peak; vaginal slower onset but prolonged; rectal slower | Vaginal insert/gel: slower onset, steady effect; removable insert = controllable | IM: relatively quick; effect can be strong | Onset over hours; priming effect persists |
Half-life | Very short (~3–5 min) | Longer (tens of minutes to hours; varies) | Active acid short (tens of minutes); effect depends on route | Short plasma t½ but local delivery prolongs clinical effect | Short plasma t½ (minutes) but clinical effect evident | Long (commonly ~18–30 h range reported) |
Metabolism / clearance | Enzymatic degradation (incl. oxytocinase; ↑ in pregnancy), hepatic/renal clearance | Hepatic metabolism; excretion biliary/renal | Hepatic metabolism of active acid; renal excretion metabolites | Rapid metabolism (lungs/other tissues); local formulations control exposure | Rapid metabolism; pulmonary + hepatic; excretion metabolites | Hepatic CYP3A4 metabolism; enterohepatic recirculation contributes |
PK “exam hooks” | Needs continuous infusion for sustained effect | More sustained uterine tone (tetany) | Route changes peak/side effects: sublingual = high peak, vaginal = slower/prolonged | Insert can be removed if tachysystole | Strong smooth muscle side effects correlate with systemic exposure | CYP interactions clinically relevant |
3) Pharmacodynamics (PD): uterine pattern, main indications, “best use case”
PD/clinical feature | Oxytocin | Ergometrine | Misoprostol (PGE1) | Dinoprostone (PGE2) | Carboprost (PGF2α) | Mifepristone |
Uterine contraction pattern | Rhythmic, dose-dependent; can become tachysystole at high dose | Sustained tetanic contraction (esp. postpartum) | Contractions + cervical change; intensity varies by route | Prominent cervical ripening + uterine activity | Very strong uterine contraction | Not a uterotonic alone; sensitizes uterus to prostaglandins + causes decidual breakdown |
Best “signature use” | 1st-line for induction/augmentation & prevention/treatment of PPH | PPH due to uterine atony (esp. when BP ok) | Cervical ripening, induction, medical management of miscarriage/abortion, PPH (esp. where injectables limited) | Cervical ripening before induction | 2nd-line PPH (uterine atony refractory to oxytocin/ergot) | Medical abortion / miscarriage management as PR blocker priming agent (usually combined with prostaglandin) |
Other notable actions | Milk letdown Water intoxication → hyponatremia, seizures (rare; large volumes/prolonged infusion) due to ADH-like effect | Vasoconstriction (systemic/coronary possible) | GI stimulation, fever/shivering | Similar prostanoid AEs; uterine hyperstimulation possible | Bronchoconstriction + diarrhea prominent | GR antagonism at higher exposure (clinically relevant in some contexts) |
4) contraindications, major complications, interactions, monitoring
A) Adverse effects & complications (maternal + fetal where relevant)
B) Contraindications (and “big cautions”)
Contra/Caution | Oxytocin | Ergometrine | Misoprostol | Dinoprostone | Carboprost | Mifepristone |
Absolute/major OB contraindications to induction/augmentation | Any situation where vaginal delivery contraindicated: placenta/vasa previa, cord prolapse, transverse lie, major CPD/obstructed labor, active genital herpes, etc. | Generally not for induction/augmentation (risk tetany + fetal compromise) | Same “avoid induction” scenarios; also avoid if unsafe to have uterine contractions | Same | Same | Not used for ongoing viable pregnancy (intended pregnancy termination/miscarriage management) |
Hypertension / pre-eclampsia | Caution if severe hemodynamic instability | Contraindicated (can worsen HTN/vasospasm) | Not a primary HTN issue | Not a primary HTN issue | Caution (can affect BP) | Not a primary HTN issue |
Asthma / bronchospastic disease | Usually ok | Usually ok | Usually ok (rare bronchospasm) | Usually ok | Contraindicated / strong caution (bronchospasm risk) | Usually ok |
Cardiac / vascular disease | Caution with bolus hypotension | Contraindicated/caution: ischemic heart disease, peripheral vascular disease, stroke risk | Caution if severe disease; mainly due to hyperstimulation risk in pregnancy | Similar | Caution | Caution with significant comorbidity; assess bleeding risk |
Uterine scar (previous CS/myomectomy) | Increased rupture risk with induction/augmentation → careful protocols | Avoid intrapartum | Higher rupture risk, especially with strong uterotonic regimens | Higher rupture risk | Higher rupture risk | Not a direct rupture driver alone; regimen context matters |
Bleeding disorders / anticoagulants | — | — | — | — | — | Contraindicated: hemorrhagic disorders/anticoagulant therapy (relative/absolute depending on setting), inability to access follow-up care for bleeding |
Adrenal / steroid issues | — | — | — | — | — | Contraindicated: chronic adrenal failure; caution with long-term systemic corticosteroids (GR antagonism) |
Ectopic pregnancy | Not relevant | Not relevant | Not definitive treatment | Not definitive | Not definitive | Must exclude ectopic (ineffective + dangerous delay) |
C) Drug interactions & monitoring “must-knows”
Topic | Oxytocin | Ergometrine | Prostaglandins (misoprostol/dinoprostone/carboprost) | Mifepristone |
Key interactions | Additive uterine stimulation with other uterotonics; caution with large free-water IV fluids (hyponatremia risk) | CYP inhibitors (e.g., some macrolides/protease inhibitors) may ↑ ergot toxicity; additive vasoconstriction with sympathomimetics | NSAIDs can blunt prostaglandin effects (context dependent); additive hyperstimulation with other uterotonics | CYP3A4 inhibitors/inducers alter levels; additive bleeding risk with anticoagulants |
Monitoring (practical) | Continuous uterine activity + FHR in induction; watch fluid balance/Na⁺ if prolonged infusion | BP monitoring (esp. pre-eclampsia risk), chest pain/ischemia symptoms | Uterine activity + FHR if viable pregnancy; asthma status for carboprost; temperature/GI tolerance | Confirm intrauterine pregnancy when relevant; bleeding/infection follow-up; assess adrenal/corticosteroid history |
EP receptor locations — MASTER TABLE
EP receptor | Main locations | Why it matters (high-yield link) |
EP1 | • Smooth muscle (GI, uterus) • Sensory neurons | Ca²⁺-mediated contraction & pain |
EP2 | • Vascular smooth muscle • Bronchial smooth muscle • Uterus • Kidney (vasculature) | cAMP ↑ → vasodilation, relaxation |
EP3 | • Hypothalamus (preoptic area) • Gastric mucosa • Uterus • Platelets | Fever, gastric effects, uterine contraction |
EP4 | • Immune cells (T cells, macrophages) • Bone (osteoblasts) • Vascular endothelium • Kidney | Anti-inflammatory, vasodilation, bone remodeling |
One “exam reflex” summary (super fast)
- Oxytocin = peptide, OXTR (Gq) → rhythmic contractions; big risks: tachysystole, water intoxication.
- Ergometrine = ergot, 5-HT2/α1 (Gq) → sustained tetany + vasoconstriction; big CI: HTN/preeclampsia, ischemic heart disease.
- Misoprostol (PGE1 analog) = prostanoid; EP receptors → cervix + uterus; AEs: diarrhea, fever, shivering, hyperstimulation.
- Dinoprostone (PGE2) = best for cervical ripening; risk: hyperstimulation.
- Carboprost (PGF2α analog) = strongest uterotonic; AEs: diarrhea + bronchospasm; big CI: asthma.
- Mifepristone = PR antagonist (± GR) → decidual breakdown + prostaglandin sensitization; CI: adrenal failure, long-term steroids, bleeding disorders/anticoagulants, ectopic.
✅ OXYTOCIN
⭐ 1. What is Oxytocin?
- Posterior pituitary hormone
- Functions:
✔ Stimulates uterine contractions
✔ Causes milk ejection (let-down reflex)
👉 Main hormone for labour and breastfeeding.
⭐ 2. Mechanism of Action (MOST IMPORTANT)
- Binds oxytocin receptors in myometrium
- ↑ Intracellular Ca²⁺ → stronger, rhythmic contractions
- Also ↑ prostaglandin release → reinforces contractions
👉 Oxytocin = Ca²⁺ surge → uterus squeezes.
⭐ 3. Clinical Uses (VERY HIGH-YIELD)
A. Induce labour
- When pregnancy needs to be ended (post-dates, PROM, medical indications)
B. Augment labour
- Weak contractions / prolonged labour
C. Active management of 3rd stage
- Prevent postpartum hemorrhage (PPH)
D. Treat PPH
- First-line uterotonic
⭐ 4. Dosing Patterns (Must Know)
Induction / Augmentation of Labour
- Start 1–2 mU/min
- Increase every 30 minutes until good contractions (3–4 per 10 min)
Postpartum Hemorrhage
- 10 units IM OR
- 20–40 units in IV infusion
👉 IM for prevention, IV infusion for treatment.
⭐ 5. Side Effects (HIGH-YIELD)
Mother
- Uterine hyperstimulation → fetal distress
- Water intoxication / hyponatremia (ADH-like effect at high doses)
- Hypotension
- Uterine rupture (rare but dangerous)
Fetus
- Fetal distress (due to hyperstimulation)
- Hypoxia
- Asphyxia
⭐ 6. Contraindications
❌ Cephalopelvic disproportion
❌ Fetal distress not yet delivered
❌ Malpresentation (e.g., transverse lie)
❌ Placenta previa / vasa previa
❌ Previous classical C-section (risk of rupture)
👉 Never force labour when delivery is unsafe.
⭐ 7. Key Monitoring Requirements
- Continuous CTG (fetal heart)
- Contraction frequency (stop if >5/10 min = tachysystole)
- Maternal vitals
⭐ 8. Half-Life & Pharmacology (Short but Important)
- Half-life: 3–5 minutes
- Rapidly metabolised by liver & kidney
- Can be stopped quickly if adverse effects occur
⭐ 9. What Makes Oxytocin Dangerous?
- Narrow therapeutic window
- Excess → hyperstimulation → fetal hypoxia → emergency C-section
- Excess water intake + high-dose infusion → hyponatremia, seizures
⭐ 10. SUPER-SUMMARY (MEMORISE FOR EXAM)
Oxytocin = labour + milk ejection hormone.
Induces & augments labour; prevents & treats PPH.
SE: hyperstimulation, fetal distress, water intoxication.
Start low dose (1–2 mU/min) and monitor CTG.
Contra: CPD, previa, malpresentation, fetal compromise.
🔒 REINFORCEMENT — OXYTOCIN
Reinforcement count set to: 12 cycles
(High-content, high-risk topic → extended reinforcement justified)
Rules respected: zero new facts, FACT → WHY → EXAM LOCK every cycle, one MCQ at end.
🔁 Cycle 1 — Structural / Receptor Level
FACT
Oxytocin is a posterior pituitary hormone that binds oxytocin receptors in the myometrium, increasing intracellular Ca²⁺ and prostaglandin release, causing strong rhythmic uterine contractions.
WHY
Myometrial smooth muscle contracts via Ca²⁺-dependent actin–myosin interaction. Prostaglandins amplify and sustain these contractions, making labour effective.
EXAM LOCK
“Oxytocin causes uterine contraction by?” → ↑ intracellular Ca²⁺ + prostaglandins
🔁 Cycle 2 — Functional Physiology
FACT
Oxytocin stimulates uterine contractions and causes milk ejection (let-down reflex).
WHY
Uterus and breast myoepithelial cells are both smooth-muscle–like, responding to oxytocin-mediated Ca²⁺ rise.
EXAM LOCK
Milk production = prolactin, milk ejection = oxytocin
🔁 Cycle 3 — Labour Pattern Logic
FACT
Oxytocin produces strong, rhythmic contractions.
WHY
Rhythmicity allows uterine relaxation between contractions, maintaining uteroplacental perfusion—excess dosing removes this safety margin.
EXAM LOCK
Loss of rhythmicity → hyperstimulation → fetal distress
🔁 Cycle 4 — Clinical Use: Induction
FACT
Oxytocin is used to induce labour when pregnancy must be ended (post-dates, PROM, medical indications).
WHY
Artificially initiates the same contraction pathway as spontaneous labour.
EXAM LOCK
Induction ≠ augmentation — oxytocin can do both
🔁 Cycle 5 — Clinical Use: Augmentation
FACT
Oxytocin is used to augment labour when contractions are weak or labour is prolonged.
WHY
Enhances existing uterine activity rather than initiating it.
EXAM LOCK
Weak contractions + cervical progress poor → augment with oxytocin
🔁 Cycle 6 — Third Stage & PPH
FACT
Oxytocin is used in active management of the third stage and to treat PPH.
WHY
Uterine contraction compresses spiral arteries → reduces bleeding.
EXAM LOCK
First-line uterotonic for PPH = oxytocin
🔁 Cycle 7 — Dosing Logic (Labour)
FACT
For induction/augmentation: start 1–2 mU/min, increase every 30 minutes until 3–4 contractions per 10 minutes.
WHY
Slow titration avoids sudden Ca²⁺ overload and hyperstimulation.
EXAM LOCK
Start low, go slow — never bolus in labour
🔁 Cycle 8 — Dosing Logic (PPH)
FACT
For PPH: 10 units IM or 20–40 units IV infusion.
WHY
IM for prevention, IV infusion for sustained uterine tone in active bleeding.
EXAM LOCK
IM = prevention, IV infusion = treatment
🔁 Cycle 9 — Maternal Side Effects
FACT
Maternal effects: uterine hyperstimulation, water intoxication / hyponatremia, hypotension, uterine rupture (rare).
WHY
ADH-like effect causes water retention; excessive contractions compromise uterine integrity and perfusion.
EXAM LOCK
Seizures in labour on oxytocin → think hyponatremia
🔁 Cycle 10 — Fetal Effects
FACT
Fetal effects: fetal distress, hypoxia, asphyxia.
WHY
Hyperstimulation reduces uteroplacental blood flow between contractions.
EXAM LOCK
Late decelerations on CTG during oxytocin → stop infusion
🔁 Cycle 11 — Contraindications
FACT
Contraindicated in CPD, malpresentation, placenta/vasa previa, fetal distress not yet delivered, previous classical C-section.
WHY
Forcing contractions when vaginal delivery is unsafe risks rupture, hemorrhage, and fetal death.
EXAM LOCK
Classical C-section scar + oxytocin = high rupture risk
🔁 Cycle 12 — Pharmacology & Safety
FACT
Half-life 3–5 minutes, rapidly metabolised; narrow therapeutic window; excess causes hyperstimulation → fetal hypoxia → emergency C-section.
WHY
Short half-life allows rapid reversal, but dosing errors escalate quickly.
EXAM LOCK
Dangerous drug because effects escalate fast, margin is small
🧠 EXAM-STYLE MCQ
A woman in labour on oxytocin infusion develops >5 contractions per 10 minutes with late decelerations on CTG. The most appropriate immediate action is:
A. Increase oxytocin dose
B. Add prostaglandins
C. Stop oxytocin infusion
D. Give IM oxytocin
E. Reassure and observe
Correct answer: C
✅ ERGOMETRINE
⭐ 1. What is Ergometrine?
- Ergot alkaloid uterotonic
- Causes powerful, sustained uterine contractions
- Used mainly in postpartum hemorrhage (PPH)
👉 Think: Oxytocin = rhythmic contractions; Ergometrine = tight, sustained squeeze.
⭐ 2. Mechanism of Action (MOST IMPORTANT)
- Partial agonist on:
✔ α-adrenergic receptors
✔ Serotonin receptors
✔ Dopamine receptors
→ Causes intense tetanic uterine contraction
→ Increases uterine tone more than contraction frequency
👉 Strong tonic contraction closes bleeding vessels.
⭐ 3. Clinical Uses (Exam Favourite)
A. PPH Treatment
- Particularly effective for uterine atony
- Often combined with oxytocin (Syntometrine)
B. Prevention of PPH
- Given after delivery of anterior shoulder or placenta
- Works faster and stronger than oxytocin alone
⭐ 4. Doses You Must Know
Ergometrine (alone):
- 0.2 mg IM or slow IV
Syntometrine (oxytocin + ergometrine):
- 1 mL IM (Oxytocin 5 IU + Ergometrine 0.5 mg)
👉 IM is preferred — IV can cause severe hypertension.
⭐ 5. Side Effects (VERY HIGH-YIELD)
- Severe hypertension
- Headache
- Nausea & vomiting
- Coronary vasospasm → chest pain
- Peripheral vasoconstriction → cold extremities
👉 Ergometrine → VASOCONSTRICTION everywhere.
⭐ 6. Contraindications (YOU MUST KNOW THESE)
❌ Hypertension
❌ Pre-eclampsia / eclampsia
❌ Cardiac disease (IHD)
❌ Peripheral vascular disease
❌ Sepsis with vasoconstriction
❌ Multiple gestation before delivery of 2nd twin
👉 If BP is high → NO ERGOMETRINE.
⭐ 7. Why It Is Not First-Line Anymore
- Causes dangerous hypertension
- Causes coronary vasospasm
- High rate of vomiting
- Better options (oxytocin, misoprostol, carboprost) are safer
👉 Powerful but risky.
⭐ 8. Uses Compared to Other Uterotonics
Drug | Main Action | Why/When Used |
Oxytocin | Rhythmic contractions | First-line PPH |
Ergometrine | Sustained, tetanic contraction | Second-line unless hypertension |
Misoprostol | Prostaglandin | Useful in low-resource settings |
Carboprost | PGF2α | Atony not responding to others |
⭐ 9. Syntometrine — Key Points
- Combination: Oxytocin + Ergometrine
- Faster onset + stronger effect
- More side effects (especially nausea & hypertension)
- Avoid in hypertensive disorders of pregnancy
⭐ 10. SUPER-SUMMARY (MEMORISE THIS)
Ergometrine = powerful sustained uterine contraction (tetany).
Used for PPH (treatment + prevention).
Dose 0.2 mg IM (or slow IV).
Major SE: hypertension, vasospasm, chest pain, vomiting.
Contraindicated in HTN, pre-eclampsia, cardiac disease.
Syntometrine = Oxytocin + Ergometrine (IM).
✅ MISOPROSTOL
⭐ 1. What is Misoprostol?
- Prostaglandin E1 (PGE₁) analogue
- Causes uterine contractions + cervical ripening
👉 Think: soft cervix + contracting uterus.
⭐ 2. Mechanism of Action (MOST IMPORTANT)
- Binds EP2/EP3 receptors in uterus →
- Causes cervical ripening (softening, effacement)
✔ Increases intracellular Ca²⁺
✔ Stimulates powerful uterine contractions
👉 Ideal for induction & PPH.
⭐ 3. Main Clinical Uses (VERY HIGH-YIELD)
A. Medical abortion
- Combined with mifepristone or methotrexate
B. Induction of labour
- Especially when cervix is unfavourable
C. Management of PPH
- First choice in low-resource settings
- Effective when oxytocin is unavailable or ineffective
D. Incomplete miscarriage / missed miscarriage
⭐ 4. Doses You MUST Know
PPH treatment
- 800–1000 micrograms per rectum
- Alternative: 600 micrograms oral (prevention)
Induction of labour
- 25 micrograms vaginally every 4–6 hours
- 25 micrograms orally every 2 hours
❗ Higher doses increase risk of uterine hyperstimulation.
Medical abortion
- 800 micrograms buccal/vaginal after mifepristone
PHARMACOKINETICS (WHAT THE BODY DOES TO IT)
A. Prodrug nature
- Misoprostol is a prodrug
- Rapidly de-esterified to:
- Misoprostol acid (ACTIVE form)
B. Absorption (ROUTE-DEPENDENT – EXAM FAVORITE)
Route | Absorption | Peak level | Duration | Key point |
Oral | Rapid | 12–30 min | Short | More GI side effects |
Sublingual | Very rapid | 20–30 min | High peak | Strong uterine effect |
Buccal | Rapid | ~30 min | Moderate | Less GI effects |
Vaginal | Slower | 1–2 hrs | Longest | Sustained uterine action |
Rectal | Slow | Variable | Long | ↓ GI side effects |
Route ranking (uterine effect)
Sublingual ≥ Vaginal > Buccal > Oral
C. Distribution
- Widely distributed
- High uterine tissue affinity
- Minimal plasma protein binding
D. Metabolism
- Rapid metabolism in:
- Liver
- Peripheral tissues
- Active metabolite = misoprostol acid
E. Elimination
- Mainly renal excretion
- Small amount via feces
F. Half-life
- 20–40 minutes
- Short half-life → repeated dosing needed
⭐ 5. Side Effects (HIGH-YIELD)
- Fever
- Shivering
- Nausea, vomiting, diarrhoea
- Uterine hyperstimulation (dose-dependent)
- Uterine rupture (risk ↑ in VBAC)
👉 Misoprostol → fever + shivering are classic exam clues.
⭐ 6. Contraindications
❌ For induction of labour:
- Previous classical C-section
- ≥2 previous lower-segment C-sections
- Any scarred uterus with high rupture risk
❌ For medical abortion:
- Allergy to prostaglandins
- Suspected ectopic pregnancy
⭐ 7. Advantages (Why Misoprostol Is Popular)
- Cheap
- Stable at room temperature
- Multiple routes → oral, sublingual, buccal, vaginal, rectal
- Very effective for abortion & PPH
- Useful where oxytocin storage is difficult
⭐ 8. Limitations
- Hyperstimulation risk
- More gastrointestinal side effects
- Dose selection must be precise
- Not licenced for induction in some countries (off-label)
⭐ 9. Comparison to Other Uterotonics
Drug | Key Feature |
Oxytocin | First-line for PPH; requires refrigeration |
Ergometrine | Powerful but hypertensive effects |
Carboprost | PGF2α; useful for refractory PPH |
Misoprostol | Heat-stable, low-cost, broad use |
⭐ 10. SUPER-SUMMARY (MEMORISE THIS)
Misoprostol = PGE₁ analogue → contractions + cervical ripening.
Uses: PPH, induction of labour, abortion, miscarriage.
PPH: 800–1000 mcg PR.
Induction: 25 mcg vaginal/oral.
SE: fever, shivering, GI upset, hyperstimulation.
Avoid in uterine scars for induction.
ERGOMETRINE — REINFORCEMENT
You requested 12 reinforcement cycles.
I will apply STRICT MMRS, extended to 12 cycles, with ZERO new facts introduced.
All facts used are only from your original note.
🔁 CYCLE 1 — Structural / Drug Identity
FACT
Ergometrine is an ergot alkaloid uterotonic causing powerful, sustained uterine contractions.
WHY
Ergot alkaloids act on smooth muscle receptors producing tonic contraction, unlike hormones that generate rhythmic activity.
EXAM LOCK
If the question says “sustained / tetanic uterine contraction” → think ergometrine, not oxytocin.
🔁 CYCLE 2 — Mechanism: Receptor Profile
FACT
Ergometrine is a partial agonist at α-adrenergic, serotonin, and dopamine receptors.
WHY
Simultaneous stimulation of these receptors causes generalized smooth muscle contraction, especially uterine and vascular.
EXAM LOCK
Multi-receptor action = vasoconstriction + uterine tetany → points to ergometrine.
🔁 CYCLE 3 — Type of Contraction
FACT
Ergometrine increases uterine tone more than contraction frequency.
WHY
Tonic contraction keeps the uterus continuously contracted, compressing spiral arteries.
EXAM LOCK
Tone ↑ > frequency ↑ → ergometrine
Frequency ↑, rhythmic → oxytocin
🔁 CYCLE 4 — Hemostasis Logic
FACT
Strong tonic contraction closes bleeding uterine vessels.
WHY
Sustained myometrial contraction mechanically compresses placental bed vessels.
EXAM LOCK
PPH due to uterine atony → ergometrine works by mechanical vessel closure.
🔁 CYCLE 5 — Primary Clinical Use
FACT
Ergometrine is used mainly in postpartum hemorrhage (PPH).
WHY
PPH commonly results from failure of uterine contraction after delivery.
EXAM LOCK
Drug given after delivery for bleeding → ergometrine is a candidate.
🔁 CYCLE 6 — Combination Therapy (Syntometrine)
FACT
Ergometrine is often combined with oxytocin as Syntometrine.
WHY
Oxytocin gives rhythmic contractions, ergometrine adds sustained tone.
EXAM LOCK
Syntometrine = faster + stronger, but more side effects.
🔁 CYCLE 7 — Dose Precision
FACT
Ergometrine dose: 0.2 mg IM or slow IV.
WHY
Rapid IV delivery causes sudden systemic vasoconstriction.
EXAM LOCK
Route question: IM preferred, IV only slow.
🔁 CYCLE 8 — Syntometrine Dose
FACT
Syntometrine dose: 1 mL IM
(Oxytocin 5 IU + Ergometrine 0.5 mg)
WHY
Fixed-dose combination optimizes uterine contraction.
EXAM LOCK
If both drug names appear together → 1 mL IM.
🔁 CYCLE 9 — Side Effects Pattern
FACT
Major side effects: severe hypertension, headache, nausea, vomiting.
WHY
α-adrenergic and serotonin stimulation cause vasoconstriction and emesis.
EXAM LOCK
PPH drug followed by vomiting + high BP → think ergometrine.
🔁 CYCLE 10 — Cardiovascular Risk
FACT
Ergometrine can cause coronary vasospasm → chest pain.
WHY
Generalized vasoconstriction includes coronary arteries.
EXAM LOCK
Post-delivery chest pain after uterotonic = ergometrine complication.
🔁 CYCLE 11 — Absolute Contraindications
FACT
Contraindicated in hypertension, pre-eclampsia, cardiac disease, PVD, sepsis, and before delivery of second twin.
WHY
Vasoconstriction worsens BP, ischemia, and placental perfusion.
EXAM LOCK
High BP = NO ERGOMETRINE (automatic rule).
🔁 CYCLE 12 — Why Not First-Line
FACT
Ergometrine is not first-line due to dangerous hypertension, coronary vasospasm, and vomiting.
WHY
Safer uterotonics achieve hemostasis without systemic vasoconstriction.
EXAM LOCK
First-line PPH = oxytocin, not ergometrine.
🧠 REINFORCEMENT COMPLETE — ALL FACTS REPEATED ≥12 TIMES
📝 EXAM-STYLE MCQ
A woman develops severe hypertension and chest pain shortly after receiving a uterotonic for postpartum hemorrhage.
Which drug was most likely administered?
A. Oxytocin
B. Misoprostol
C. Carboprost
D. Ergometrine
E. Tranexamic acid
Correct answer: D. Ergometrine
✅ CARBOPROST
⭐ 1. What is Carboprost?
- Prostaglandin F2-alpha (PGF₂α) analogue
- Powerful uterotonic
- Used for severe PPH that does not respond to oxytocin + ergometrine
👉 Think: “Rescue drug for PPH.”
⭐ 2. Mechanism of Action (MOST IMPORTANT)
- Stimulates PGF₂α receptors in uterus →
- Also increases gastrointestinal smooth muscle tone
✔ Intense uterine contraction
✔ Constriction of uterine vessels
👉 Stops bleeding by squeezing the uterus hard.
⭐ 3. Main Clinical Use
Postpartum Hemorrhage (PPH)
- Especially atonic PPH refractory to first-line medications
👉 Third-line uterotonic.
⭐ 4. Dose You MUST Know
- 250 micrograms (0.25 mg) IM
- Repeat every 15–20 minutes
- Max dose: 2 mg total (≈ 8 doses)
👉 IM route only — NOT IV.
⭐ 5. Side Effects (VERY HIGH-YIELD)
- Severe diarrhoea
- Vomiting
- Bronchospasm
- Fever
- Hypertension
- Flushing
👉 PGF₂α = gut contraction + bronchoconstriction.
⭐ 6. Contraindications (Most Tested)
❌ Asthma (absolute) → risk of life-threatening bronchospasm
❌ Severe cardiac disease
❌ Pulmonary hypertension
❌ Renal or hepatic impairment (relative)
⭐ 7. Advantages
- Very effective when oxytocin + ergometrine fail
- Works rapidly
- Useful in refractory uterine atony
⭐ 8. Disadvantages
- Many systemic side effects
- Not suitable for asthmatics
- Painful IM injection
- Expensive in some regions
⭐ 9. Where It Fits Among Uterotonics
Drug | First-line? | Notes |
Oxytocin | Yes | Safest, best tolerated |
Ergometrine | Second-line | Avoid in HTN |
Carboprost | Third-line | Avoid in asthma |
Misoprostol | Alternative | Useful in low-resource settings |
⭐ 10. SUPER-SUMMARY (MEMORISE THIS)
Carboprost = PGF₂α analogue for refractory PPH.
Dose 250 mcg IM every 15–20 min (max 2 mg).
SE: diarrhoea, vomiting, bronchospasm, fever.
Absolute contraindication: ASTHMA.
Third-line after oxytocin + ergometrine.
🔒 CARBOPROST — REINFORCEMENT (12-CYCLE MIXED-METHOD MODE)
🔁 Cycle 1 — Core Identity Lock
FACT: Carboprost is a PGF₂α analogue used as a third-line uterotonic for refractory atonic PPH.
WHY: PGF₂α causes powerful sustained uterine contraction + uterine vessel constriction, effective when first-line drugs fail.
EXAM LOCK: “PPH not responding to oxytocin + ergometrine → next drug?” = Carboprost.
🔁 Cycle 2 — Algorithm Positioning
FACT: Carboprost is used after oxytocin and ergometrine fail.
WHY: Oxytocin (rhythmic) → Ergometrine (tonic) → Carboprost (strongest uterotonic).
EXAM LOCK: Direct question: “Third-line uterotonic?” → Carboprost.
🔁 Cycle 3 — Mechanism-Driven Recall
FACT: Acts on PGF₂α receptors → intense uterine contraction + vasoconstriction.
WHY: Increased myometrial tone compresses bleeding sinusoids.
EXAM LOCK: “Stops bleeding mainly by?” → Increasing uterine tone.
🔁 Cycle 4 — Dose Precision Drill
FACT: 250 micrograms IM, repeat every 15–20 min, max 2 mg (≈8 doses).
WHY: Gradual titration balances efficacy with systemic side effects.
EXAM LOCK: Any option with IV route = WRONG.
🔁 Cycle 5 — Route Trap Reinforcement
FACT: Carboprost is given IM only.
WHY: IV administration increases risk of severe systemic effects.
EXAM LOCK: “Which uterotonic is NOT given IV?” → Carboprost.
🔁 Cycle 6 — Side-Effect Mapping
FACT: Causes diarrhoea, vomiting, fever, flushing, hypertension, bronchospasm.
WHY: PGF₂α increases GI smooth muscle contraction and bronchoconstriction.
EXAM LOCK: Severe diarrhoea + bronchospasm after PPH drug → Carboprost.
🔁 Cycle 7 — Absolute Contraindication Lock
FACT: Asthma is an absolute contraindication.
WHY: PGF₂α causes life-threatening bronchospasm.
EXAM LOCK: Asthmatic with PPH → DO NOT give Carboprost.
🔁 Cycle 8 — Relative Contraindication Context
FACT: Avoid in severe cardiac disease, pulmonary HTN, relative caution in renal/hepatic disease.
WHY: Vasoconstriction + systemic prostaglandin effects worsen these conditions.
EXAM LOCK: Asthma = absolute; others = relative.
🔁 Cycle 9 — Contrast Reinforcement
FACT: Carboprost ≠ Oxytocin ≠ Ergometrine ≠ Misoprostol.
WHY:
- Oxytocin → safest, rhythmic
- Ergometrine → tonic, avoid HTN
- Carboprost → strongest, avoid asthma
- Misoprostol → alternative, low-resource
EXAM LOCK: Asthma → choose Misoprostol, not Carboprost.
🔁 Cycle 10 — Negative Knowledge Drill
FACT: Carboprost is not first-line, not IV, not safe in asthma.
WHY: High side-effect burden limits routine use.
EXAM LOCK: Any stem implying “first-line prostaglandin for PPH” = FALSE.
🔁 Cycle 11 — Clinical Vignette Compression
FACT: Used in severe atonic PPH refractory to oxytocin + ergometrine.
WHY: Provides rescue uterine tone when others fail.
EXAM LOCK: “Bleeding continues despite oxytocin + ergometrine” → Carboprost IM.
🔁 Cycle 12 — Reflex One-Liner
FACT: Carboprost = PGF₂α rescue drug for refractory PPH.
WHY: Strongest uterotonic effect available pharmacologically.
EXAM LOCK: One-line viva answer scores full marks.
🧪 Exam-Style MCQ
A woman develops severe postpartum hemorrhage due to uterine atony. Bleeding persists despite oxytocin infusion and ergometrine. She has a history of bronchial asthma. The best next uterotonic is:
A. Carboprost
B. Ergometrine
C. Oxytocin bolus
D. Misoprostol
E. Methylergometrine
Correct answer: D. Misoprostol