Oxytocin
Chemical
Synthetic peptide hormone
Use
Induction labour
PPH
Lactation
Presentation
5-10IU/ml Syntocin
5IU/ml oxytocin + 500mcg ergometrine
Dose
1.5-12mUnits/min titrated to frequency of contractions (IV)
1ml of oxytocin+ergometrine (IM)
Route
IM/IV
Onset
IV – immediate
IM – 4 mins
DoA
1h (IV)
2-3h(IM)
MoA
Binds Oxytocin receptors lining uterus
GqPCR → IP3/DAG → increase intracellular Ca++ → increase amplitude & frequency of contractions
High dose = sustained contractions w incomplete relaxation & impaired uterine/placental BF
Contraction of myoepithelial cells surrounding alveoli of breasts to facilitate lactation
PD
CVS – hypotension, tachycardia, reduced coronary perfusion
RENAL – V2 agonism, ADH-like effects; H2O retention, hyponatraemia
ENDO – lactation
PK
A
Inactivated orally
D
PPB 30%
Vd – crosses placenta & breast milk
M
Rapid liver metabolism by oxytocinases
E
Biliary & renal (excreted unchanged in urine)
Adverse Effects
Severe H2O intoxication due to antidiuretic effect
Convulsions, coma, death
Fetal asphyxia
DI: interacts w SUX (required higher dosing)
Cannot be administered w blood products – rapid hydrolysis