Vasopressor Pharmacology

David Ray Velez, MD

Comparison

	α-1	α-2	β-1	β-2	D	Effects
*Midodrine*	X					BP
*Phenylephrine*	X					BP
*Norepinephrine*	X		(Some)			BP
*Epinephrine*	High	High	Low	Low		Heart (Low) and BP (High)
*Dopamine*	High	High	Med	Med	Low	Renal (Low), Heart (Med), and BP (High)
*Dobutamine*			X	(Some)		Heart
*Isoproterenol*			X	X		Heart
*Vasopressin*	Primarily V-1 (Vasoactive)					BP
*Angiotensin II*	AT-1 and AT-2 (RAAS System)					BP
*Milrinone*	PDE Inhibitor					Contractility and Pulmonary Vasodilation

Adrenergic Receptors

α-1: Vascular Smooth Muscle Constriction (Increase Blood Pressure)
α-2: Venous Smooth Muscle Constriction
β-1: Heart (Increase Heart Rate and Contractility)
β-2: Vascular Smooth Muscle Relaxation and Bronchial Smooth Muscle Relaxation (Decrease Blood Pressure)
β-3: Relax Bladder and Increases Lipolysis in Adipose Tissue
- Unrelated to Cardiovascular System
Adrenergic Effects Can Be Blunted by Hypoxia, Acidosis, and Persistent Sympathetic Activation

Other Receptors

Dopamine Receptors: Renal and Splanchnic Smooth Muscle Relaxation
Vasopressin Receptors:
- V-1 Receptor: Arterial Vasoconstriction
- V-2 Receptor: Renal Water Resorption
- V-3 Receptor: Mediates Factor VIII and vWF Release

Midodrine

Phenylephrine (Neo-Synephrine)

Receptors: α-1
Effects: Increased Blood Pressure
General Dosing:
- Weight Based: 0.1-1.5 mcg/kg/min
- Non-Weight Based: 10-200 mcg/min
May Cause Baroreceptor-Mediated Reflex Bradycardia (Due to Sole Alpha Stimulation)

Norepinephrine (Levophed)

Receptors: α-1 and β-1
- β-1 Effects are Less Pronounced at Higher Doses
Effects: Increased Blood Pressure
- Also Causes Splanchnic Vasoconstriction
- β-1 Effects Can Cause Increased Heart Rate and Risk for Atrial Fibrillation
General Dosing:
- Weight Based: 0.05-2.0 mcg/kg/min
- Non-Weight Based: 2-64 mcg/min

Epinephrine (Adrenaline)

Low-Dose (0.1-0.3 mcg/kg/min):
- Receptors: β-1 and β-2
- Effects: Increased Contractility but May See Decreased Blood Pressure
High-Dose (0.3-1.0 mcg/kg/min):
- Receptors: α-1 and α-2
- Effects: Vasoconstriction and Increased Blood Pressure

Dopamine

Low-Dose (1-2 mcg/kg/min):
- Receptors: Dopamine Receptors
- Effects: Splanchnic Vasodilation (“Renal Dose Dopamine”)
Medium-Dose (2-10 mcg/kg/min):
- Receptors: β-1
- Effects: Positive Inotropy
High-Dose (10-20 mcg/kg/min):
- Receptors: α-1
- Effects: Vasoconstriction and Increased Blood Pressure

Dobutamine

Receptors: β-1 (Primarily) and β-2 (Some)
Effects: Increased Contractility and Heart Rate
- Blood Pressure May Decrease Due to Vasodilation
General Dosing: 1-20 mcg/kg/min
Greatly Increases Cardiac Oxygen Consumption and Can Potentiate Ischemia and Ventricular Arrhythmias

Isoproterenol (Isoprenaline)

Receptors: β-1 and β-2
Effects: Increased Contractility and Heart Rate
- Blood Pressure May Decrease Due to Vasodilation
General Dosing: 2-10 mcg/min
Greatly Increases Cardiac Oxygen Consumption and Can Potentiate Ischemia and Ventricular Arrhythmias

Arginine Vasopressin (AVP)

Angiotensin II

Receptors: AT-1 and AT-2
- Part of the RAAS System
Effects: Vasoconstriction and Increased Blood Pressure
- Also Activates Adrenal Cortex to Stimulate Aldosterone Secretion
- Also Activates Hypothalamus to Stimulate Vasopressin Secretion
General Dosing: 5-80 ng/kg/min

Milrinone