Learning Objective
Identify the major clinical uses of norepinephrine and epinephrine and explain why indirect-acting adrenergic agonists are ineffective in denervated tissues.
Shared Uses
Both norepinephrine and epinephrine can be used for:
Cardiac Arrest
- Provide potent β1 stimulation → increases heart rate, conduction, and contractility.
- Essential in advanced cardiac life support (ACLS).
Adjunct to Local Anesthetics
- Mainly, epinephrine is used, but NE has been used historically.
- α1-mediated vasoconstriction → reduces systemic absorption → prolongs anesthetic effect → reduces bleeding.
Hypotension
- Particularly norepinephrine, due to strong α1 vasoconstriction → ↑ systemic vascular resistance → ↑ BP.
- Used in septic shock as first-line.
Activity
Epinephrine ONLY
These uses depend on β2 effects, which norepinephrine lacks.
Anaphylaxis
First-line drug: Mechanisms:
- Bronchodilation (β2)
- ↑ BP via α1 vasoconstriction
- ↑ cardiac output via β1
- Stabilizes mast cells (β2)
Asthma (acute)
- β2 bronchodilation → relaxes bronchial smooth muscle.
- Less commonly used now due to the availability of selective β2 agonists (e.g., albuterol).
Activity
Clinical Correlate
Clinical example:
After surgical denervation or peripheral neuropathy, indirect sympathomimetics do not affect the target organ.
