Oxytocics classify uses adverse effect ; enumerate clinical indications of each agents ; Oxytocin and prostaglandin analogues compare and contrast as oxytocics; Oxytocin and ergometrine compare and contrast ; Why is oxytocin used for induction of labor and not methylergometrine; Ergometrine inPPH pharmacological basis, contraindications to use if ergometrine 2nd yr mbbs pharmacology refer kd tripathi answers in details with flowcharts and diagrams as well
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KD Tripathi oxytocics classification ergometrine oxytocin prostaglandins pharmacology 2nd year MBBS
Here is your complete, exam-oriented guide to Oxytocics for 2nd year MBBS, aligned with KD Tripathi Chapter 23.
OXYTOCICS - Complete 2nd Year MBBS Pharmacology Guide
(KD Tripathi, Ch. 23: Oxytocin and Other Drugs Acting on Uterus)
1. CLASSIFICATION OF OXYTOCICS
┌─────────────────────────────────────────────────────────────┐
│ OXYTOCICS │
│ (Drugs that stimulate the uterus) │
└────────────────────────┬────────────────────────────────────┘
│
┌─────────────────┼─────────────────┐
▼ ▼ ▼
┌──────────────┐ ┌──────────────┐ ┌─────────────────────┐
│ POSTERIOR │ │ ERGOT │ │ PROSTAGLANDINS │
│ PITUITARY │ │ ALKALOIDS │ │ │
│ HORMONE │ │ │ │ PGE2: Dinoprostone │
│ │ │ Ergometrine │ │ PGF2α: Carboprost │
│ Oxytocin │ │ Methyl- │ │ (15-me-PGF2α) │
│ (Syntocinon │ │ ergometrine │ │ PGE1: Misoprostol │
│ Pitocin) │ │ (Methergine) │ │ (Cytotec) │
└──────────────┘ └──────────────┘ └─────────────────────┘
2. MECHANISM OF ACTION
OXYTOCIN
────────────────────────────────────────────────────────────
Oxytocin → Oxytocin receptor (Gq-coupled GPCR)
│
▼
Phospholipase C activated
│
┌─────┴─────┐
▼ ▼
IP3 ↑ DAG ↑
│ │
▼ ▼
Ca²⁺ release PKC activation
from SR
│
└───────────► Myosin Light Chain Kinase (MLCK)
│
▼
Myosin phosphorylation
│
▼
UTERINE CONTRACTION
Also: stimulates PGF2α / PGE2 production from decidua
────────────────────────────────────────────────────────────
ERGOMETRINE
────────────────────────────────────────────────────────────
Ergometrine → α-adrenoceptor + 5-HT2 receptor agonist
on uterine smooth muscle
│
▼
Sustained TETANIC contraction
(no relaxation phase between contractions)
────────────────────────────────────────────────────────────
PROSTAGLANDINS
────────────────────────────────────────────────────────────
PGE2/PGF2α → EP / FP receptors (Gq-coupled GPCR)
│
▼
Ca²⁺ mobilization (IP3 pathway)
│
▼
Uterine contraction + cervical ripening/softening
(PGE2 = best cervical ripener)
3. CLINICAL INDICATIONS OF EACH AGENT
A. Oxytocin
┌──────────────────────────────────────────────────┐
│ CLINICAL USES OF OXYTOCIN │
├──────────────────────────────────────────────────┤
│ 1. Induction of labour (DOC - drug of choice) │
│ - Post-dates pregnancy (>42 weeks) │
│ - Pre-eclampsia / eclampsia │
│ - Diabetes mellitus in pregnancy │
│ - IUFD (intrauterine fetal death) │
│ - PROM (premature rupture of membranes) │
│ 2. Augmentation of dysfunctional labour │
│ 3. Active management of 3rd stage of labour │
│ (prevents PPH) │
│ 4. Treatment of PPH (uterine atony) - 1st line │
│ 5. Oxytocin challenge test (OCT) │
│ - Tests uteroplacental reserve │
│ 6. Milk let-down (intranasal spray) │
├──────────────────────────────────────────────────┤
│ Dose (induction): 0.5-2 mU/min IV, titrate to │
│ max 20-40 mU/min │
│ Dose (PPH): 10U IM; or 20-40U in 500mL saline │
└──────────────────────────────────────────────────┘
B. Ergometrine / Methylergometrine
┌──────────────────────────────────────────────────┐
│ CLINICAL USES OF ERGOMETRINE │
├──────────────────────────────────────────────────┤
│ 1. PPH - PRIMARY USE (atonic PPH after placental │
│ delivery; 2nd line after oxytocin) │
│ 2. Active management of 3rd stage of labour │
│ (combined with oxytocin = Syntometrine) │
│ 3. Subinvolution of uterus (postpartum) │
│ 4. Incomplete/inevitable abortion (lochia) │
│ 5. To hasten uterine involution │
├──────────────────────────────────────────────────┤
│ NOT used for induction of labour! │
│ Dose: 0.2 mg IM (or IV in emergency only) │
└──────────────────────────────────────────────────┘
C. Prostaglandins
┌──────────────────────────────────────────────────┐
│ CLINICAL USES OF PROSTAGLANDINS │
├──────────────────────────────────────────────────┤
│ PGE2 (DINOPROSTONE) │
│ 1. Cervical ripening (unfavorable cervix) │
│ - Intravaginal gel/pessary/tablet │
│ 2. Induction of labour at term │
│ 3. 2nd trimester abortion / IUFD │
│ │
│ PGF2α (CARBOPROST = 15-methyl-PGF2α) │
│ 1. Refractory PPH (after oxytocin + ergometrine │
│ have failed) │
│ 2. 2nd trimester MTP (abortion) │
│ Dose: 250 mcg IM every 15-90 min, max 8 doses │
│ │
│ PGE1 (MISOPROSTOL - Cytotec) │
│ 1. Medical abortion (+ mifepristone) │
│ 2. Cervical ripening / labour induction │
│ 3. PPH prevention/treatment (when refrigeration │
│ unavailable - resource-limited settings) │
│ 4. Missed/incomplete abortion │
│ 5. Peptic ulcer (gastric cytoprotection) │
│ Dose (PPH): 600-1000 mcg sublingual/rectal │
└──────────────────────────────────────────────────┘
4. ADVERSE EFFECTS
Oxytocin
┌──────────────────────────────────────────────────────────┐
│ ADVERSE EFFECTS - OXYTOCIN │
├──────────────────────────────────────────────────────────┤
│ UTERINE │
│ • Uterine hyperstimulation (>5 contractions/10 min) │
│ • Uterine rupture (esp. scarred/multipara uterus) │
│ • Fetal distress (late decelerations on CTG) │
│ • Placental abruption │
│ │
│ CARDIOVASCULAR (at high doses) │
│ • Hypotension (vasodilation) │
│ • Reflex tachycardia │
│ • Especially dangerous with rapid IV bolus │
│ │
│ ANTIDIURETIC (ADH-like cross-activation at high doses) │
│ • Water retention → hyponatremia │
│ • Water intoxication → convulsions, coma, death │
│ (particularly with excess hypotonic IV fluids) │
│ │
│ OTHERS │
│ • Nausea, vomiting │
│ • Hypersensitivity (rare) │
└──────────────────────────────────────────────────────────┘
Ergometrine
┌──────────────────────────────────────────────────────────┐
│ ADVERSE EFFECTS - ERGOMETRINE │
├──────────────────────────────────────────────────────────┤
│ CARDIOVASCULAR │
│ • Hypertension (vasoconstriction via α-agonism) │
│ • Coronary vasospasm → angina, MI │
│ • Peripheral vasospasm → gangrene (overdose) │
│ │
│ GI │
│ • Nausea, vomiting (prominent) │
│ │
│ CNS │
│ • Headache, dizziness │
│ • Seizures (ergotism - overdose) │
│ │
│ UTERINE (if given at wrong time) │
│ • Sustained tetanic contraction → fetal asphyxia │
│ • Retained placenta (if given before delivery) │
│ │
│ ERGOTISM (chronic/overdose) │
│ • Gangrene of extremities (vasoconstriction) │
│ • Convulsions │
└──────────────────────────────────────────────────────────┘
Prostaglandins
┌──────────────────────────────────────────────────────────┐
│ ADVERSE EFFECTS - PROSTAGLANDINS │
├──────────────────────────────────────────────────────────┤
│ • Nausea, vomiting, diarrhea (most common - GI smooth │
│ muscle stimulation) │
│ • Uterine hyperstimulation → fetal distress │
│ • Fever, chills, rigors (esp. carboprost) │
│ • BRONCHOSPASM (PGF2α / Carboprost) │
│ → Contraindicated in asthma │
│ • Headache, flushing (vasodilation) │
│ • Hypotension (PGE2 dinoprostone) │
│ • Uterine rupture (rare, misoprostol in scarred uterus)│
└──────────────────────────────────────────────────────────┘
5. COMPARE: OXYTOCIN vs PROSTAGLANDIN ANALOGUES
| Feature | Oxytocin | Prostaglandins (PGE2, PGF2α, PGE1) |
|---|---|---|
| Source | Posterior pituitary (nonapeptide) | Synthesized from arachidonic acid (eicosanoids) |
| Receptor | Oxytocin receptor (Gq-coupled) | EP/FP receptors (GPCR) |
| Mechanism | Gq → PLC → IP3 → Ca²⁺ | Gq → PLC → IP3 → Ca²⁺ (also cAMP via EP2/EP4) |
| Type of contraction | Rhythmic, phasic (like physiological labour) | Rhythmic but also sustained; acts at all gestational ages |
| Cervical ripening | NO (minimal) | YES - hallmark of PGE2 and misoprostol |
| Gestational age dependence | Near term only (needs estrogen-primed receptors; receptor density increases 200-300x during pregnancy) | Effective at ALL gestational ages |
| Route | IV infusion, IM, intranasal | Vaginal, intracervical, oral, sublingual, rectal |
| Induction of labour | DOC - 1st line | Used for cervical ripening first, then oxytocin continues |
| PPH management | 1st line (10U IM) | 2nd-3rd line (carboprost for refractory PPH) |
| Half-life | 5-12 min (IV) | Seconds (natural); minutes-hours (synthetic analogues) |
| BP effect | Vasodilation → hypotension (high dose) | Variable: PGE2 vasodilates; PGF2α vasoconstricts |
| Antidiuretic effect | YES (V2 receptor cross-activation) | No |
| GI side effects | Mild | Prominent (N/V/D) |
| Bronchospasm | No | YES (PGF2α/Carboprost) - CI in asthma |
| 2nd trimester MTP | Not effective | YES - misoprostol + mifepristone (DOC) |
| Storage | Requires cold chain (refrigeration) | Misoprostol stable at room temperature - advantage in field settings |
| Cost | Moderate | Misoprostol - very cheap; dinoprostone - expensive |
6. COMPARE: OXYTOCIN vs ERGOMETRINE
| Feature | Oxytocin | Ergometrine / Methylergometrine |
|---|---|---|
| Source | Posterior pituitary (peptide hormone) | Ergot fungus (Claviceps purpurea) - alkaloid |
| Chemical nature | Nonapeptide | Ergot alkaloid (lysergic acid derivative) |
| Receptor | Oxytocin receptor (Gq-GPCR) | α-adrenergic + 5-HT2 receptors |
| Type of contraction | Rhythmic, PHASIC (with relaxation between contractions) | Sustained TETANIC (no relaxation) |
| Analogy | Like normal uterine contractions | Like a clenched fist that never opens |
| BP effect | Vasodilation → hypotension | Vasoconstriction → HYPERTENSION |
| Induction of labour | YES - DOC | NEVER (tetanic = fetal asphyxia + rupture) |
| PPH | 1st line | 2nd line (or concurrent) |
| 3rd stage | 10U IM after anterior shoulder | ONLY after placental delivery |
| Antidiuretic effect | YES (at high doses) | No |
| Half-life | 5-12 min | 1-2 hours (much longer) |
| Onset (IM) | 3-5 min | 2-7 min |
| Route | IV infusion, IM | IM, oral (methylergometrine); IV only in emergency |
| Titratable | YES (IV infusion easily adjusted) | NO (fixed IM dose; cannot be quickly reversed) |
| Cardiac risk | Hypotension, reflex tachycardia | Coronary vasospasm → angina/MI |
| Key CI | Fetal malpresentation, fetal distress, placenta praevia | Hypertension, pre-eclampsia, heart disease |
| Combined form | Syntometrine = 5U Oxytocin + 0.5 mg Ergometrine IM | (same) |
7. WHY OXYTOCIN FOR INDUCTION - NOT METHYLERGOMETRINE
CONTRACTION PATTERN COMPARISON:
OXYTOCIN (SAFE for induction):
Uterine
tone ▲
│ ╭──╮ ╭──╮ ╭──╮ ╭──╮
│ ╭╯ ╰╮ ╭╯ ╰╮ ╭╯ ╰╮ ╭╯ ╰╮
─────┼──╯ ╰───╯ ╰───╯ ╰───╯ ╰──
└──────────────────────────────────────► time
Rhythmic phasic contractions
(with relaxation phase between them)
↑ Blood flow restored during relaxation
↑ Fetus oxygenated between contractions
METHYLERGOMETRINE (DANGEROUS for induction):
Uterine
tone ▲▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬
│
─────┼──────────────────────────────────────► time
Sustained tetanic contraction
(NO relaxation = NO blood flow restoration)
↓ Fetoplacental blood flow → fetal hypoxia
↓ Risk of uterine rupture
| Reason | Oxytocin (safe) | Methylergometrine (unsafe) |
|---|---|---|
| Contraction type | Phasic with relaxation - preserves fetoplacental blood flow | Tetanic, no relaxation - blood flow cut off |
| Fetal oxygenation | Maintained during relaxation | Severely compromised → fetal asphyxia |
| Uterine rupture | Low risk with monitoring | High risk - unrelenting contraction |
| Titratable/reversible | Short t½ (5-12 min) - stop infusion to reverse | Duration 1-2 hrs; cannot be quickly reversed |
| BP effect | Vasodilation - manageable | Hypertension - dangerous in preeclampsia |
| Cervical effect | Gradual cervical dilation with contractions | May cause cervical laceration |
Memory key: "Oxytocin = Oscillating (rhythmic) = safe for labour. Ergometrine = Eternal contraction (tetanic) = only AFTER delivery."
8. ERGOMETRINE IN PPH: PHARMACOLOGICAL BASIS
Why Does PPH Occur? Why Does Ergometrine Help?
POSTPARTUM - Normal hemostasis:
Placenta delivered
│
▼
Uterus must CONTRACT
│
▼
Myometrial fibers compress sinusoidal vessels
│
▼
"LIVING LIGATURE" effect = hemostasis
──────────────────────────────────────────────────
IN ATONIC PPH:
Uterus FAILS to contract (uterine atony)
│
▼
Sinusoidal vessels remain OPEN
│
▼
Massive hemorrhage from placental bed
(can lose 500-1000+ mL/minute)
──────────────────────────────────────────────────
HOW ERGOMETRINE TREATS PPH:
Ergometrine 0.2 mg IM
│
▼
α-adrenergic + 5-HT2 receptor activation
on myometrium
│
▼
SUSTAINED TETANIC CONTRACTION of entire uterus
│
▼
Myometrium physically COMPRESSES intramural vessels
│
▼
"LIVING LIGATURE" restored
│
▼
BLEEDING STOPS
KEY: The tetanic contraction that is DANGEROUS during
labour (risks fetus + rupture) is BENEFICIAL in PPH
because: fetus is delivered, placenta is out -
sustained contraction = maximum hemostasis
Pharmacological basis summary:
- Ergometrine acts on α-adrenergic and 5-HT2 receptors to cause sustained, powerful uterine contraction
- The contraction physically occludes the open sinusoidal/spiral arteries at the placental bed
- This is called the "living ligature" - contracted myometrial fibers act like ties around the bleeding vessels
- Onset is rapid (IM 2-7 min, IV 40 seconds) and effect lasts 1-2 hours - sustained hemostasis
- The longer duration vs oxytocin (5-12 min) means less chance of rebleeding
9. CONTRAINDICATIONS TO ERGOMETRINE
┌─────────────────────────────────────────────────────────┐
│ CONTRAINDICATIONS TO ERGOMETRINE │
├─────────────────────────────────────────────────────────┤
│ │
│ CARDIOVASCULAR (ergometrine raises BP) │
│ • Hypertension - ANY cause (most important CI) │
│ (causes further dangerous BP rise → stroke) │
│ • Pre-eclampsia / Eclampsia │
│ • Heart disease (ischemic, valve disease) │
│ (coronary vasospasm → MI) │
│ • Peripheral vascular disease │
│ • Raynaud's phenomenon │
│ │
│ OBSTETRIC (wrong timing = catastrophe) │
│ • First stage of labour (baby in utero - fetal risk) │
│ • Second stage of labour (same reason) │
│ • Before placental delivery │
│ (tetanic contraction traps placenta │
│ → retained placenta → worse PPH!) │
│ • Multiple pregnancy (2nd twin may be trapped) │
│ • Malpresentation │
│ │
│ OTHER │
│ • Hepatic impairment (impaired metabolism) │
│ • Renal impairment │
│ • Sepsis │
│ • Induction/augmentation of labour (wrong indication) │
│ │
└─────────────────────────────────────────────────────────┘
MEMORY AID - "HIPPER MC":
H - Hypertension
I - Induction of labour (contraindicated)
P - Pre-eclampsia
P - Placenta not yet delivered
E - Eclampsia
R - Raynaud's / cardiac/peripheral vascular disease
M - Multiple pregnancy
C - Coronary artery disease
10. MASTER FLOWCHART: OXYTOCICS IN OBSTETRIC PRACTICE
CLINICAL SITUATION
│
├──► INDUCTION OF LABOUR ─────────────────────────┐
│ │
│ Is cervix favorable (Bishop score >6)? │
│ │ │
│ NO ├──► PGE2 (Dinoprostone) / │
│ │ Misoprostol (PGE1) │
│ │ → Cervical ripening first │
│ │ │ │
│ │ ▼ │
│ YES └──► OXYTOCIN IV infusion (DOC) │
│ 0.5-2 mU/min, titrate │
│ up to 20 mU/min max │
│ │
├──► ACTIVE MANAGEMENT 3RD STAGE ─────────────────┤
│ │
│ After delivery of anterior shoulder: │
│ Oxytocin 10U IM OR │
│ Syntometrine (Oxytocin 5U + │
│ Ergometrine 0.5mg) IM │
│ → ONLY after placenta delivered for ergom. │
│ │
└──► POSTPARTUM HEMORRHAGE (PPH) ─────────────────┘
PPH STEPWISE MANAGEMENT:
┌─────────────────────────────────────────────────────────┐
│ STEP 1: Oxytocin 10U IM + uterine massage │
│ (+20-40U in IV infusion) 1st line │
│ │ │
│ ▼ (not controlled) │
│ STEP 2: Ergometrine 0.2mg IM 2nd line │
│ (IF not hypertensive, no eclampsia) │
│ │ │
│ ▼ (not controlled) │
│ STEP 3: Carboprost (PGF2α) 250mcg IM 3rd line │
│ repeat q15-90 min (max 8 doses) │
│ (IF not asthmatic) │
│ │ │
│ ▼ (not controlled) │
│ STEP 4: Misoprostol 600-1000mcg sublingual/rectal │
│ │ │
│ ▼ (not controlled) │
│ STEP 5: Surgical/interventional (B-Lynch suture, │
│ uterine artery ligation, hysterectomy) │
└─────────────────────────────────────────────────────────┘
QUICK EXAM SUMMARY TABLE
| Drug | Receptor | Contraction | Key Use | Key AE |
|---|---|---|---|---|
| Oxytocin | OT-R (Gq) | Rhythmic phasic | Labour induction (DOC); PPH 1st line | Water intoxication; Hypotension |
| Ergometrine | α + 5-HT2 | Sustained TETANIC | PPH 2nd line; 3rd stage | Hypertension; Coronary spasm |
| Dinoprostone (PGE2) | EP (Gq) | Rhythmic + cervix ripening | Cervical ripening; Induction | N/V/D; Hypotension |
| Carboprost (PGF2α) | FP (Gq) | Sustained; all ages | Refractory PPH; 2nd trim MTP | Bronchospasm (CI asthma); Fever |
| Misoprostol (PGE1) | EP1/EP3 | Rhythmic + cervix | MTP; PPH (resource-limited); Induction | N/D; Uterine hyperstim |
References:
- KD Tripathi: Essentials of Medical Pharmacology, 8th Ed., Ch. 23 (Oxytocin and Other Drugs Acting on Uterus)
- Goodman & Gilman's Pharmacological Basis of Therapeutics, 14th Ed.
- Katzung Basic & Clinical Pharmacology, 16th Ed., Ch. 37
- Creasy & Resnik's Maternal-Fetal Medicine, 9th Ed.
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