Vasopressin (20units) is a sterile, aqueous solution of synthetic arginine vasopressin, a nonapeptide hormone identical to the natural human antidiuretic hormone (ADH). It is a potent vasoconstrictor and antidiuretic agent. In the Indian clinical context, it is a critical drug used in advanced cardiac life support (ACLS) for vasopressor support during cardiac arrest, and in the management of gastrointestinal bleeding, particularly esophageal variceal hemorrhage. It is also used for diabetes insipidus, though desmopressin is often preferred for this indication due to a more favorable side effect profile.
Adult: Cardiac Arrest (ACLS): 40 units IV push once. Alternative to first or second dose of epinephrine. Variceal Bleeding: 0.2-0.4 units/min IV infusion, titrated up to a max of 0.8-0.9 units/min. Often combined with IV nitroglycerin. Diabetes Insipidus: 5-10 units IM/SC every 6-8 hours, adjusted based on urine output and osmolality.
Note: For IV infusion: Must be diluted in Normal Saline or 5% Dextrose. Common dilution: 100 units (5 ampoules of 20 units) in 500 mL NS (0.2 units/mL). Use an infusion pump. For IV push in arrest: Administer undiluted or diluted in 10-20 mL NS. IM/SC: Administer undiluted. Avoid extravasation (can cause severe tissue necrosis). Central line administration is preferred for continuous infusion.
Vasopressin exerts its effects by binding to specific G-protein coupled receptors: V1a (vascular/hepatic), V1b (pituitary), and V2 (renal). The V1a receptor activation on vascular smooth muscle stimulates phospholipase C, increasing intracellular inositol triphosphate (IP3) and diacylglycerol (DAG), leading to calcium mobilization and potent vasoconstriction, especially in the splanchnic, cutaneous, and coronary beds. V2 receptor activation in the renal collecting ducts increases water permeability via aquaporin-2 channel insertion, promoting water reabsorption (antidiuresis).
Pregnancy: Category C: Animal studies show adverse effects. Use only if potential benefit justifies potential fetal risk. Can stimulate uterine contractions. Monitor for fetal distress.
Driving: May cause dizziness, vertigo. Patients should be cautioned about operating machinery or driving until their response is known.
| Carbamazepine, Chlorpropamide, Clofibrate, NSAIDs | Potentiate antidiuretic effect, increasing risk of water intoxication/hyponatremia. | Major |
| Lithium, Demeclocycline | Antagonize antidiuretic effect, reducing efficacy in diabetes insipidus. | Major |
| Ganglionic blocking agents (e.g., Trimethaphan) | Increased pressor sensitivity, risk of severe hypertension. | Major |
| Nitroglycerin, Other Nitrates | Used together in variceal bleeding to reduce ischemic side effects; may require careful titration to maintain BP. | Moderate |
| Catecholamines (Epinephrine, Norepinephrine) | Additive vasoconstrictive effects; increased risk of severe hypertension, ischemia, arrhythmias. | Major |
| Halothane, Cyclopropane | Increased risk of arrhythmias (less relevant with modern anesthesia). | Moderate |
Same composition (Vasopressin (20units)), different brands: