Oxytocics: Induction and Augmentation of Labor
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Transcript of Oxytocics: Induction and Augmentation of Labor
Oxytocin and Ergot Derivatives
Oxytocics
“Drugs of varying chemical nature that have the power to excite contractions of the uterine muscles”
Three groups exist: I. OxytocinII. Ergot derivativesIII. Prostaglandins
Chemistry
A nona peptide
Meaning: Quick Birth
Similar in structure to vasopressin
In nonmammalian vertebrates vasotocin performs both functions
PhysiologySupraoptic and paraventricular nucleus
Transported by fast axonic transport bound to proteins called neurophysins (Prohormone)
Prohormone converted during transport
Also secreted by the decidua, luteal cells of the ovary and extraembryonic fetal tissue
Oxytocin receptors increase 30 fold while the sensitivity increases 8 fold mostly during the last 9 weeks prior to delivery
Secretion is stimulated by sensory stimuli from cerivcal and vaginal dilatation
Estradiol also increases secretion
Inhibited by relaxin: mediated via endogenous opioids
Factors that primarily affect vasopressin secretion also have some impact on oxytocin release
Released in bursts during labour
Oytocin during Parturition
Contd...
A cysteine aminopeptidase in the plasma rapidly metabolises oxytocin A short halflife of 3 10 mins Fetal oxytocin production increases during active
laborNo evidence regarding entry of oxytocin into maternal circulation
Short halflife may explain the need for fetal oxytocin secretion
Initiation Of Parturition
Parturition has three phases*
Phase 0 : Phase of uterine quiescence
Phase 1 : Preparation for labor
Phase 2 : Labor and delivery
Phase 3 : Puerperium
Phase 1: Gap junction formation between smooth muscles of uterus and synthesis of oxytocin receptor
Oxytocin was believed to initiate parturition, current evidence states otherwise
*N.B. : Parturition is said to begin on transion from phase 0 to phase 1
Oxytocin during Puerperium
Oxytocin likely causes persitent uterine contraction preventing PPH
Oxytocin infusion increases mRNAs of genes that encode proteins needed for uterine involution : Interstitial collagenase, monocyte chemoattractant protein1, IL8 and urokinase plasminogen activator receptor
Oxytocin during Lactation
Oxytocin in Daily Life
Research indicates oxytocin has a role in various behaviours, including social recognition, pair bonding, anxiety, maternal behaviours, libido etc...
So the hormone is called “love hormone”
Inability to secrete this hormone is linked to sociopathy, psychopathy and general manipulativeness
Mechanism of Action
Gprotein coupled receptors connected to phosholipase C cascade
Also causes local synthesis and release of PGF2α
Physiological uterine contraction fundal contraction; cervical relaxation
PharmacokineticsPreparations:
Synthetic oxytocin (Syntocinon, Pitocin) 5IU/ml amp
Syntometrine (Sandoz Syntocinon 5U+Ergometrine 0.5mg)
Desamino oxytocin Buccal tablet 50 I.U. (long halflife)
Oxytocin nasal spray – 40U/ml
Buccal and nasal spray – limited use
Circulating halflife 3 10 mins
Duration of action: 20 – 30 minutes
Excreted through liver and kidney
Stored at 2 – 8º C
Therapeutic Indications
Pregnancy Puerperium
Early (2nd Trimester) Late
Induce abortion
Accelerate abortion
Terminate molar pregnancy
Labor Induction
Labor Augmentation
Uterine Inertia
Manage third stage
of labor
Minimize blood loss
Control Post Partum
Hemorrhage
Diagnostic IndicationsContraction stress test
Oxytocin sensitivity test
CONTRAINDICATIONS
Fetal Causes
Severe hydrocephalus
MalpresentationNonreassuring fetal heart rate
Maternal Causes
Grand multipara Prior uterine rupture Previous classical section Placenta praevia major CPD Active genital herpes or
cancer cervix
DOSAGE & ADMINISTRATION
Induction & Augmentation
2 regimens:
Low dose regimenHigh dose regimen
Regimen Starting dose (mU/min)
Incremental increase (mU/min)
Dosage interval (min)
Low dose 2.5
5
2.5
5
30
30
High dose 6 6,3,1 1540
Table 1. Oxytocin regimens for stimulation of labour
Low dose regimen
Drops/min ml/min Total amount of fluid in 30 min (ml)
Dose/min (mIU/min)
8 0.5 15 2.5
16 1 30 5
24 1.5 45 7.5
32 2 60 10
40 2.5 75 12.5
48 3 90 15
56 3.5 105 17.5
64 4 120 20
72 4.5 135 22.5
Table 2. Flow and Dosage of Oxytocin Solution*
N.B. : 2.5 IU syntocinon is added to 500 ml of RL to obtain 5 mIU/ml concentration
Results are unsatisfactory then add 5 IU of syntocinon to 500 ml of RL
therefore, 10mIU/ml
Drops/min ml/min Total amount of fluid in 30 min (ml)
Dose/min (mIU/min)
32 2 60 20
40 2.5 75 25
48 3 90 30
56 3.5 105 35
64 4 120 40
72 4.5 135 45
Table 3. Flow and dosage of Oxytocin Solution
• Maximum licensed dose = 20 mIU/min
• Max dose that can be given = 4045 mIU/min
• Time taken for the completion of the above regimen is 6 ½ hrs
• N.B.: most of the women deliver with the dose of 12 mIU/min
High dose regimen
Indicated in pregnant women in whom the volume overload is dangerous
Advantages over low dose regimen1. Shorter mean admission to delivery time2. Fewer failed induction3. Fewer cases of neonatal sepsis/ chorioamnionitis4. Fewer incidence of forceps delivery/caesarean
section
Duration of Administration
End point
• Adequate uterine contractions i.e., 34 / 10 min, each lasting for 3540 seconds
• Satisfactory descent of the presenting part
• Satisfactory dilatation of the cervix i.e., atleast 1cm/hr
End point
2.5/6 mIU/minAugmentation
30 minutes
Monitoring*
Maternal pulse and BP, hourly
Frequency, Intensity and duration of uterine contractions, halfhourly
Fetal Heart Rate, halfhourly
To combat uterine hyperstimulation, injection 0.25 mg terbutaline s.c. is used
* N.B.: Best done using partogram
Oxytocin Challenge Test
Also called Contraction Stress Test
This test checks for uteroplacental circulation deficiency
Contractions are induced using I.V. Oxytocin infused initially at the rate of 1mU/min and step raised every 20 min. till end point of adequate contraction is achieved.
Fetal heart rate response and contraction rate and intensity are recorded
Contd...Contraindications
Compromised fetus
Multiple pregnancy
H/O caesarean section
Antepartum hemorrhage
Complications likely to produce preterm labor
Candidates
Intra Uterine Growth Restricted mothers
Post maturity
Diabetes
Hypertensive disorders of pregnancy
Interpretation
Positive test : Persistent FHR* deceleration
Negative test : No late FHR deceleration
Suspicious : Inconsistent but definite decelerations which do not persist with every uterine contraction
Unsatisfactory : Poor recording quality and/or inadequate uterine contraction
Hyperstimulation : Deceleration of FHR with each uterine contraction lasting > 90 min. Or with frequency of contraction being more than one every 2 min. (5 every 10 minutes)
Oxytocin Sensitivity Test
Assess irritability of uterus to oxytocin
Procedure :
0.01U given IV at the end of spontaneous contractionRepeated at 1min interval until induced contraction starts (hardening)
Inference :
If contraction does not begin after 4 injections then uterus is unlikely to be responsive to induction
Adverse Reactions & Complications
Uterine hyperstimulation
Hypertonia (each contraction > 60sec)
Polysystole (>6/10 min)
Uterine rupture
Water intoxication*
Occurs with rates 3040 mIU/min
Due to vasopressin like activity
Hypotension ( iv bolus) : Due to temporary vasodilation caused by oxytocin
Fetal distress (due to hyperstimulation)
* N.B.: Don't infuse more than 1 L fluid in 24 hours
Lactation and Pregnancy
No large scale study is available to arrive at definite conclusions Oxytocin released during lactation will cause mild
uterine contractions Mother is protected as oxytocin receptors are not
present till late in pregnancy
The American Academy of Family Physicians states that “If the pregnancy is normal and the mother is healthy,
breastfeeding during pregnancy is the woman' s personal decision”
Ergot Derivatives
Natural alkaloid obtained from fungi Claviceps purpura, that grows in rye
Therapeutically useful alkaloid are amide derivatives of dlysergic acid
Semisynthetic derivatives are obtained from catalytic hydrogenation of the natural alkaloids. e.g. Methergin (methylergonovine)
E.g.: Ergometrine Alkaloid from Ergot
Methergin – Semisynthetic product from Lysergic acid
Preparations Available
Parenteral: Prefered route
Ergometrine 0.5 mg IM, 0.5 mg IV
Methergin 0.2mg IV
Oral : Rapidly absorbed, peaks at 60 – 90 min
Ergometrine 0.5 – 1 mg tab
Methergin 0.5 – 1 mg tab
Metabolism
Ergotamine is metabolised in liver by undefined pathways
90% metabolites : excreted in bile
Traces seen in urine and feces
Ergometrine is metabolised and excreted more rapidly than ergotamine
Plasma halflife : 30 – 120 minutes
Duration of action : 3 hrs
Mechanism of Action
Acts through serotonin receptors (5HT 2) and αadrenergic receptors
During pregnancy, the uterine sensitivity to ergot increases dramatically
Causes uniform contraction of uterus (nonphysiological)
In very small doses can cause rythmic contraction of uterus
Ergonovine is more selective in affecting uterus
Indications*
Prophylactic: Prevent post partum hemorrhage – given as IV 0.2mg methergin after anterior shoulder delivery
Control bleeding after delivery (instrumental or caesarean section or abortion)
*N.B. : Ergot derivatives must never be used prior to delivery for induction or augmentation of labor
Contraindications
Multiple pregnancy
Preeclampsia / Eclampsia
Rhnegative mother
Cardiac disease
Severe hypertension
Adverse Effects
Gastro Intestinal symptoms : Nausea, Vomitting, Diarrhoea – Activation of medullary vomitting centre and GI serotonin receptors
Overdosage : Prolonged vasospasm – gangrene of toes requiring amputation (rare)
Bowel infarction has been reported (very rare)
Interferes with lactation
Can precipitate MI, Stroke, Bronchospasm & raise of BP (Vasoconstriction effects)
Oxytocin Ergot derivatives
Mechanism of action Acts on physiological uterine contraction system
Acts directly on muscle cells causing contraction
Onset of action Slower Faster
Duration Long sustained Short lived
Uses
1) Prophylactically stop hemorrhage postpartum2) Stop hemorrhage after
instrumental delivery, etc...
1) Induction of labor2) Augmentation of labor
3) Stop Post Partum Hemorrhage
Adverse effectsGI symptoms, rise in BP, Stroke, Gangrene of toes
(rare), etc..
Uterine Hyperstimulation, Antidiuresis, Uterine
rupture, etc...