1. Clinical Overview
Vasopressin (20IU) is a synthetic analogue of the endogenous antidiuretic hormone (ADH), arginine vasopressin. It is a potent vasoconstrictor and antidiuretic agent, primarily used in critical care settings in India for the management of vasodilatory shock, gastrointestinal bleeding, and during certain surgical procedures. It acts on V1 receptors in vascular smooth muscle to cause vasoconstriction and on V2 receptors in renal collecting ducts to promote water reabsorption.
| Onset | Duration | Bioavailability |
|---|---|---|
| Rapid; within minutes of intravenous administration. | Short; approximately 30 to 60 minutes for pressor effects; antidiuretic effect lasts 2-8 hours. | Negligible via oral route; 100% via intravenous (IV) route. |
2. Mechanism of Action
Vasopressin is an agonist at vasopressin receptors (V1, V2, and V3). Its primary therapeutic effects in critical care are mediated through V1 receptors on vascular smooth muscle, leading to potent vasoconstriction, especially in the splanchnic, cutaneous, and coronary beds. This increases systemic vascular resistance and mean arterial pressure. At higher doses, it also activates V2 receptors in the renal collecting ducts, increasing water permeability via aquaporin-2 channels, leading to antidiuresis.
3. Indications & Uses
- Vasodilatory shock (e.g., septic shock, post-cardiotomy shock) as an adjunct to catecholamines
- Control of bleeding from esophageal varices (used with endoscopic therapy)
- During certain types of cardiac arrest (as per ACLS guidelines, though epinephrine is first-line)
4. Dosage & Administration
Adult Dosage: Vasodilatory Shock: 0.01-0.04 units/minute as continuous IV infusion. Titrate to target MAP. Esophageal Varices: 0.2-0.4 units/minute IV infusion, may be increased to 0.8 units/minute if bleeding continues. Cardiac Arrest: 40 IU as a single IV/IO bolus (replaces first or second dose of epinephrine).
Administration: MUST BE DILUTED before IV administration. For infusion: Dilute 20 IU in 100 mL of Normal Saline or 5% Dextrose to a concentration of 0.2 units/mL. Administer via a central venous catheter preferred to avoid peripheral tissue necrosis. Use an infusion pump. Monitor blood pressure, heart rate, ECG, urine output, and signs of peripheral ischemia continuously.
5. Side Effects
Common side effects may include:
- Pallor
- Nausea, abdominal cramps
- Headache
- Sweating
- Tremor
- Fluid retention, hyponatremia (with prolonged use)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Catecholamines (Noradrenaline, Adrenaline) | Additive/synergistic pressor effects; increased risk of severe hypertension and cardiac arrhythmias. | Major |
| Ganglion-blocking agents (e.g., Trimethaphan) | Markedly increased pressor sensitivity to vasopressin. | Major |
| Carbamazepine, Chlorpropamide, NSAIDs | May potentiate the antidiuretic (V2) effect, increasing risk of water intoxication and hyponatremia. | Moderate |
| Heparin | Vasopressin may partially counteract the anticoagulant effect of heparin. | Moderate |
| Lithium, Demeclocycline | Antagonize the antidiuretic effect of vasopressin. | Moderate |
| Alcohol | Inhibits vasopressin secretion; may reduce antidiuretic effect. | Minor |
7. Patient Counselling
- This medication will be administered by healthcare professionals in a hospital.
- Report immediately any chest pain, shortness of breath, severe headache, or numbness/coldness in limbs.
- Inform the doctor of all other medications you are taking.
8. Toxicology & Storage
Overdose: Manifestations include hypertension, bradycardia, arrhythmias, myocardial ischemia/infarction, severe peripheral vasoconstriction leading to gangrene, water intoxication (headache, drowsiness, confusion, seizures, coma), hyponatremia, nausea, abdominal cramps, and uterine cramps.
Storage: Store unopened vials at 2°C to 8°C (refrigerate). Do not freeze. Protect from light. After dilution, the solution is chemically stable for up to 24 hours at room temperature. However, it should be used immediately due to microbiological risk. Do not use if solution is discolored or contains particulate matter.