Vasopressin (Antidiuretic Hormone)

Vasopressin is the antidiuretic hormone used medicinally for both renal water-conserving and vasopressor effects. Its principal emergency veterinary role is support of vascular tone in selected vasodilatory shock or resuscitation settings. Selected central diabetes insipidus and diagnostic applications also occur, although other hormone preparations are more commonly used for sustained antidiuretic treatment.

Group

Antidiuretic hormone and vasopressor

Mechanism of Action

Vasopressin activates V1 receptors on vascular smooth muscle, increasing intracellular calcium signaling and producing vasoconstriction. At renal collecting-duct V2 receptors, cyclic-AMP signaling promotes insertion of aquaporin-2 water channels and increases water reabsorption. These distinct receptor actions account for pressor and antidiuretic effects. The dominant clinical effect depends on exposure and treatment context.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Antidiuretic therapy	10 IU/animal	IV, IM		Desmopressin preferred; repeat frequency unspecified.
Vasodilatory shock	Reference only	IV		IV rate 0.01-0.04 IU/min with absolute ceiling 0.04 IU/min, also described as 0.5-5 milliunits/kg/min. These are not equivalent for every weight; enforce absolute rate ceiling. Fixed-rate and weight-based alternatives must not be treated as equivalent.
Cardiopulmonary resuscitation	0.8 IU/kg	IV	As needed	Bolus may be repeated during resuscitation; no repeat interval is specified.
Cardiopulmonary resuscitation alternative	0.2–0.8 IU/kg	IV	Once

Cats

Use / stage	Dose	Route	Schedule	Instructions
Antidiuretic therapy	10 IU/animal	IV, IM		Desmopressin preferred; repeat frequency unspecified.
Vasodilatory shock	Reference only	IV		IV rate 0.01-0.04 IU/min with absolute ceiling 0.04 IU/min, also described as 0.5-5 milliunits/kg/min. These are not equivalent for every weight; enforce absolute rate ceiling. Fixed-rate and weight-based alternatives must not be treated as equivalent.
Cardiopulmonary resuscitation	0.8 IU/kg	IV	As needed	Bolus may be repeated during resuscitation; no repeat interval is specified.
Cardiopulmonary resuscitation alternative	0.2–0.8 IU/kg	IV	Once
Vasopressin response diagnostic test	0.5 IU/kg	IM	Once	Only within a controlled diabetes-insipidus diagnostic protocol; water-deprivation testing is contraindicated with dehydration or renal disease.

Indications

Adjunctive vasopressor treatment of selected refractory vasodilatory shock in veterinary patients.
Vasopressor support during cardiopulmonary resuscitation in dogs and cats within an appropriate contemporary resuscitation protocol.
Short-term antidiuretic replacement in selected central diabetes insipidus cases.

Contraindications

Water retention and excessive vasoconstriction require individualized monitoring.

Adverse effects

Hypertension and hypersensitivity are possible.

Toxicity

Excess antidiuretic action can cause water intoxication, depression, seizures or coma. Stop treatment and assess sodium, osmolality and fluid balance urgently; avoid unmonitored water changes.

Preparations

Preparation	Form	Strength	Route
Vasopressin aqueous injection 20 IU/mL	Injection	20 IU / mL	IV, IM

Monitoring and Administration

Dilute IV infusion in saline and titrate against perfusion. Reported targets systolic pressure 100-120 mmHg and urine output 0.5-1.5 mL/kg/hour, individualized to patient.

For antidiuretic therapy, monitor water intake, urine output, specific gravity and sodium; desmopressin is preferred for chronic central diabetes insipidus.

Canine vasopressin-response protocol uses 2.5 milliunits/kg (0.0025 IU/kg) in D5W over one hour with staged bladder emptying and urine collection after water-deprivation endpoint. The printed specific-gravity threshold 1.1015 is inconsistent with the comparison 1.015; this diagnostic interpretation is not normalized. Do not use vasopressin for cardiogenic shock; fixed 0.04 IU/min upper shock rate must be respected.