What is the recommended dosage of vasopressin and how is it calculated?

Vasopressin Dosing and Calculation

Vasopressin is administered as a continuous IV infusion at 0.03 units/minute (not weight-based) when added to norepinephrine in septic shock, with a dosing range of 0.01-0.07 units/minute, and should never exceed 0.04 units/minute except as salvage therapy. 1, 2

Clinical Context-Specific Dosing

Septic Shock (Most Common Indication)

• Start at 0.03 units/minute as a fixed-dose continuous infusion when norepinephrine alone fails to maintain MAP ≥65 mmHg despite adequate fluid resuscitation 1, 2
• The dose range is 0.01-0.07 units/minute, but doses above 0.03-0.04 units/minute should be reserved only for salvage therapy when all other vasopressors have failed 1, 2
• Vasopressin is NOT weight-based—use the same 0.03 units/minute dose regardless of patient size 1, 3
• Never use vasopressin as monotherapy or first-line agent—it must be added to norepinephrine, not replace it 1, 2

Variceal Hemorrhage in Cirrhosis

• Start at 0.2-0.4 units/minute continuous IV infusion, which can be increased to a maximum of 0.8 units/minute 4, 2
• Must always be accompanied by IV nitroglycerin starting at 40 µg/minute (up to 400 µg/minute) to reduce ischemic complications and maintain systolic blood pressure ≥90 mmHg 4
• Maximum duration is 24 hours due to high risk of cardiac, peripheral, and bowel ischemia 4

Calculation Method

There is no calculation required—vasopressin dosing is fixed, not calculated based on weight or body surface area:

• For septic shock: Simply set the infusion pump to deliver 0.03 units/minute 1, 2
• For variceal bleeding: Set the infusion pump to deliver 0.2-0.4 units/minute initially 4

Practical Infusion Preparation

• Standard concentration: Mix 100 units vasopressin in 250 mL normal saline = 0.4 units/mL 5, 6
• For 0.03 units/minute: Set pump at 4.5 mL/hour (0.03 units/min ÷ 0.4 units/mL × 60 min/hour) 5, 6

Critical Safety Considerations

Absolute Requirements Before Starting

• Central venous access is mandatory for administration 1
• Arterial catheter placement for continuous blood pressure monitoring should be established as soon as practical 1
• Ensure adequate fluid resuscitation (minimum 30 mL/kg crystalloid) has been completed 1

Dose-Related Toxicity Thresholds

• Doses above 0.04 units/minute carry significant risk of cardiac arrest, digital ischemia, and splanchnic ischemia 1, 6
• If MAP targets are not achieved at 0.03 units/minute vasopressin plus norepinephrine, add epinephrine as a third agent rather than increasing vasopressin dose 1
• Monitor for signs of excessive vasoconstriction: digital ischemia, decreased urine output, rising lactate, abdominal pain, or chest pain 1, 2, 6

Common Pitfalls to Avoid

• Never titrate vasopressin like other vasopressors—it is used at a fixed low dose, not titrated to effect 1, 7
• Do not use weight-based dosing (e.g., units/kg/min)—conflicting data exist on weight impact, and guidelines recommend fixed dosing 1, 3
• Avoid using vasopressin for "renal protection"—this has no proven benefit 1
• Do not use terlipressin (long-acting vasopressin analog) if patient has ongoing coronary, peripheral, or mesenteric ischemia, or worsening respiratory symptoms 2
• When weaning vasopressors in resolving shock, discontinue vasopressin last (not second-to-last) to reduce rebound hypotension 3

Alternative Agents When Vasopressin Unavailable

• Terlipressin 2 mg IV every 4 hours (can be reduced to 1 mg every 4 hours once bleeding controlled) for variceal hemorrhage—has longer duration and fewer side effects than vasopressin 4
• Epinephrine 0.05-2 mcg/kg/min as alternative second-line vasopressor in septic shock 1