Vasopressin in 0.9% Sodium Chloride Injection

Vasopressin in 0.9% Sodium Chloride Injection is an IV vasopressor solution (a synthetic form of the hormone arginine vasopressin) premixed in normal saline. It comes in sterile 100 mL bags containing either 20 units or 40 units of vasopressin (i.e. 0.2 U/mL or 0.4 U/mL). This ready-to-use infusion raises blood pressure by constricting blood vessels (vasoconstriction), since vasopressin binds V1 receptors on vascular smooth muscle. It also has an antidiuretic (water-retaining) effect via kidney V2 receptors. In practice, this drug is used only in severe shock when standard measures have failed.

Indications and Use

Vasopressin infusion is indicated for adults in vasodilatory shock (like septic shock or post-cardiotomy shock) whose blood pressure remains dangerously low despite adequate IV fluids and catecholamine vasopressors. In other words, after giving IV fluids and drugs such as norepinephrine or epinephrine, if the patient is still hypotensive, vasopressin can be added to increase vascular tone. The typical starting infusion rates are about 0.01–0.03 units/minute (for example, 0.01 U/min in septic shock, 0.03 U/min in post-cardiac surgery shock). The rate is then titrated slowly upward (by ~0.005 U/min every 10–15 minutes) until the desired blood pressure is reached. Label guidance notes that doses above about 0.07 U/min (septic shock) or 0.1 U/min (post-op shock) have little data and may increase side effects. (When BP is stable for many hours on vasopressin – usually after other pressors have been stopped for ≥8 hours – the infusion can be tapered by ~0.005 U/min per hour.)

• Formulation: Each 100 mL bag is a single-dose premix (0.9% NaCl plus vasopressin, pH~3.6–4.0). No further dilution is required before use. Do not add other medications to the bag.
• Channels of administration: Give only by continuous IV infusion (preferably via a dedicated central line, given potency). Infuse with a calibrated pump. Ensure the IV line is patent and free of kinks.
• Preparation: Inspect the bag visually – it should be clear and colorless. Discard if discolored or cloudy. Prime the line and start the infusion at the ordered rate. After use, discard any unused solution (the containers are single-use). Treat this like other sterile infusions (aseptic prep, label date/time, etc.).

Mechanism of Action

Vasopressin is a nonapeptide that acts on V1 receptors in vascular smooth muscle to cause vasoconstriction. By increasing intracellular calcium, it narrows blood vessels throughout the body (arteries, veins, splanchnic circulation, skin, etc.), which raises systemic vascular resistance and increases mean arterial pressure. This effect is additive when used with catecholamine pressors. Vasopressin also acts on V2 receptors in the kidney, retaining water and concentrating urine; this property can dilute serum sodium during the infusion and then cause a diuretic rebound when the drug is stopped.

Dosage and Administration (Summary)

• Starting dose: typically 0.01–0.03 units/min by IV infusion, depending on the shock type.
• Titration: increase by 0.005 U/min every 10–15 minutes if needed, up to ~0.07 U/min in sepsis (or 0.1 in post-cardiac shock). Titrate to the lowest effective dose.
• Infusion setup: Use the strength on the bag to set the pump. For example, a 20 U/100 mL bag (0.2 U/mL) at 0.03 U/min is ~0.15 mL/min (9 mL/hr).
• No additives: This product is “ready-to-use.” Do not add diluents or mix other drugs. Do not use as an IV push or bolus.
• Duration: Continue infusion as long as needed for hypotension. If the patient stabilizes, taper gradually.

Side Effects and Precautions

• Hypotension/cardiac effects: Paradoxically, vasopressin can reduce cardiac output and even worsen heart function, because it increases afterload. Common adverse events include bradycardia, tachyarrhythmias, and decreased cardiac output. Use caution in patients with coronary artery disease or heart failure. Monitor ECG and hemodynamics continuously.
• Ischemia: Vasopressin may constrict blood flow to some organs. Documented effects include skin and peripheral ischemia, mesenteric (gut) ischemia, and coronary ischemia. Watch for severe limb pain, mottling, abdominal pain, or chest pain. If these occur, reassess need for vasopressin.
• Electrolytes/Water balance: Because of its antidiuretic action, vasopressin commonly causes hyponatremia (water retention) while on the drug. Conversely, after stopping the infusion, patients may develop diabetes insipidus–type diuresis (excess urine, dilute urine, rising sodium) as the hormone effect reverses. Monitor serum sodium, fluid balance, and urine output. Be prepared to replace fluids or electrolytes as needed.
• Extravasation: As a potent vasoconstrictor, vasopressin can cause severe tissue injury if the IV line leaks. Ensure IV patency. (If extravasation occurs, infuse phentolamine or nitroglycerin at the site as you would for other pressors.)
• Allergy: Do not give to patients with known allergy to vasopressin.
• Pregnancy: Vasopressin can induce uterine contractions and harm the fetus. Use extreme caution in pregnant patients (normally this drug would only be used if life-threatening shock requires it).
• Pediatrics: Safety and dosing in children have not been established for this product, so use in pediatrics is not generally recommended.
• Drug interactions: Pressor effects are additive with other vasopressors. Indomethacin and other NSAIDs can prolong vasopressin’s effect (by blocking its clearance). Drugs that cause SIADH (SSRIs, haloperidol, etc.) may add to its effect. Drugs that antagonize ADH (lithium, demeclocycline) may reduce its pressor effect. Always review the patient’s medications.

Storage and Handling

Store the unopened infusion bag refrigerated at 2–8°C (36–46°F). Protect it from light and freezing. If needed, the bag may be kept at room temperature (up to 25°C) for no more than 6 months. After 6 months out of refrigeration, or after the printed expiration date, discard the bag. Once warmed, do not re-refrigerate the bag. Use within 24 hours of opening (discard any unused portion).

In summary: Vasopressin in 0.9% Sodium Chloride Injection is a sterile, premixed IV vasopressor for critical hypotension that does not respond to fluids and catecholamines. It works by strong vasoconstriction via V1 receptors. It requires careful titration in an ICU setting, with vigilant monitoring for bradycardia, ischemia, or electrolyte disturbances. Adherence to dosing and storage instructions (ready-to-use bag, no dilution, refrigerated storage) is essential.