Vasopressin

Mechanism of action

Acts as antidiuretic and vasopressor via arginine vasopressin (AVP) receptors, increasing reabsorption of free water, systemic vascular resistance and mean arterial blood pressure. This may lead to reflex bradycardia.

• V1 vascular smooth muscle of the systemic, splanchnic, renal, and coronary circulations -> potent vasoconstriction
  - vasoconstriction of renal efferent arterioles -> increased GFR

• V2 renal collecting ducts -> anti-diuresis
  - haemostatic system -> induces the release of Von Willebrand Factor (VWF) and Factor VIII:coagulant (FVIII:c) from endothelial cells -> increased platelet    aggregation

• V3 pituitary -> stimulates release of ACTH and hence increased cortisol secretion
  ‍
• less pulmonary artery vasoconstriction than noradrenaline, may even cause pulmonary artery vasodilation
• less arrhythmia than noradrenaline

Indications and dose

Side-effects

Splanchnic vasoconstriction

Uterine contraction

Ischaemia and necrosis on extravasation

Oliguria

Water intoxication

Reflex bradycardia

Pharmacokinetics

Onset: Vasopressor effect within 15 minutes; Antiduretic effect 1-2 hours

Duration:  Vasopressor: 20 minutes; Antidiuretics: 2-8 hours

Metabolism: Hepatic and renal (peptidases)

Half-life of elimination: 10-20 minutes

Excretion: Urine

Directions for administration

For intravenous infusion dilute in 5% glucose. Suggested concentration is 20-40 units/50 ml.

Administer e.g. 20 Units in 50 ml 5% glucose - 1.5-6 ml/hour.

Medicinal forms

1 vial = 20 units in 1 ml

1 vial = 40 units in 2 ml

‍References

1. https://bnf.nice.org.uk/drugs/vasopressin/ 
2. https://www.medicines.org.uk/emc/product/4117/smpc#gref 
3. https://litfl.com/vasopressin/ 
4. https://www.uptodate.com/contents/vasopressin-drug-information?search=vasopressin&source=panel_search_result&selectedTitle=1~148&usage_type=panel&kp_tab=drug_general&display_rank=1#F233576