Vasopressin

Vasopressin, also known as antidiuretic hormone (ADH), is a peptide hormone synthesized in the hypothalamus and stored in the posterior pituitary gland. It plays a critical role in regulating water retention in the kidneys and maintaining vascular tone. As a medication, vasopressin is utilized in various clinical settings, including vasodilatory shock, diabetes insipidus, gastrointestinal bleeding, and cardiac arrest.

Uses

Vasodilatory Shock: Used in septic and vasodilatory shock unresponsive to catecholamines to increase blood pressure through vasoconstriction.
Diabetes Insipidus: Treats central diabetes insipidus by reducing urine output and controlling fluid balance.
Gastrointestinal Bleeding: Manages esophageal variceal bleeding by reducing portal pressure.
Cardiac Arrest: Acts as an alternative to epinephrine in advanced cardiac life support (ACLS) during resuscitation.
Hemodynamic Support: Used in post-cardiotomy shock to improve hemodynamics.

Dosage and Administration

Vasodilatory Shock:

IV Infusion: 0.01-0.04 units/min, titrate based on blood pressure response.

Cardiac Arrest (ACLS):

IV/IO: 40 units as a single dose, can replace the first or second dose of epinephrine in adult cardiac arrest.

Diabetes Insipidus:

IM/Subcutaneous: 5-10 units 2-4 times daily as needed.
Intranasal: 10-40 mcg daily, divided into 1-3 doses.

Esophageal Variceal Bleeding:

IV: 0.2-0.4 units/min infusion. Adjust to control bleeding.

Dose Adjustment in Different Diseases

Hepatic Impairment: Monitor closely; metabolism may be altered.
Renal Impairment: Adjust dose or increase monitoring due to reduced excretion.
Elderly: Use with caution due to increased risk of hyponatremia and ischemia.
Cardiac Disease: Lower doses may be required to reduce the risk of myocardial ischemia.

Drug Combinations in Use

Catecholamines (e.g., norepinephrine): Enhances vasopressor effects.
Corticosteroids: May improve outcomes in shock management.
Diuretics: Increased risk of hyponatremia when combined with vasopressin.
Carbamazepine, Chlorpropamide, Clofibrate, Tricyclic Antidepressants: Potentiate the antidiuretic effect.

Presentation or Form

Injection: 20 units/mL in 1 mL ampoules or vials.
Intranasal Spray: Available for use in diabetes insipidus.

Pharmacokinetics

Onset: Immediate with IV use.
Duration: 30-60 minutes for IV administration; longer duration with subcutaneous use.
Half-life: 10-20 minutes when given intravenously.
Metabolism: Primarily in the liver and kidneys.
Excretion: Renal and hepatic.

Pharmacodynamics

V1 Receptors: Located on vascular smooth muscle, cause vasoconstriction and increase blood pressure.
V2 Receptors: Located in the renal collecting ducts, promote water reabsorption and reduce urine output.
V3 Receptors: Located in the anterior pituitary, stimulate ACTH release.

Drug Interactions

Catecholamines: Enhances vasopressor effects.
Corticosteroids: May enhance vasopressor effects.
Diuretics: Risk of hyponatremia.
Potentiators: Carbamazepine, chlorpropamide, clofibrate, tricyclic antidepressants.
Antagonists: Lithium and demeclocycline may reduce vasopressin efficacy.

Comparison with Other Drugs of Same Category

Drug	Mechanism of Action	Indications	Onset (IV)	Half-life (IV)	Key Side Effects
Vasopressin	V1 and V2 receptor agonist	Shock, DI, bleeding	Immediate	10-20 min	Hyponatremia, ischemia
Desmopressin	Selective V2 agonist	DI, bleeding disorders	30 min	1-2 hours	Headache, hyponatremia
Terlipressin	V1 receptor agonist	Variceal bleeding	30 min	4-6 hours	Ischemia, abdominal pain

Precautions and Special Considerations

Cardiovascular Disease: Increased risk of myocardial ischemia.
Elderly: Higher risk of adverse effects, especially hyponatremia.
Seizure Disorders: Use with caution.
Pregnancy: Category C; use only if the potential benefit justifies the risk.
Extravasation: Monitor for tissue necrosis at infusion sites.

Side Effects

Common:

Abdominal cramps
Nausea
Headache

Serious:

Hyponatremia
Arrhythmias
Ischemia (myocardial, mesenteric, or peripheral)
Tissue necrosis at infusion site

Less Common:

Water intoxication
Allergic reactions
Bronchial constriction

Recent Updates and Guidelines

2023 ACC/AHA Guidelines: Vasopressin recommended as an adjunct to norepinephrine in septic shock when MAP remains below target.
Evolving ACLS Protocols: Emphasis on epinephrine as first-line, with vasopressin reserved for specific cases.
New Formulations: Development of slow-release intranasal formulations for diabetes insipidus management.

Facts to Remember

Vasopressin can be life-saving in vasodilatory shock and refractory cardiac arrest.
Monitor serum sodium and urine output to avoid hyponatremia.
Extravasation requires immediate treatment to prevent tissue necrosis.
Use cautiously in patients with coronary artery disease or seizure disorders.
Continuous monitoring of hemodynamics is essential during administration.