V2i: Oxytocin

Oxytocin

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