A9. Catecholamines

Question 1

What are cathecholamines?

Answer 1

Catecholamines are post-synaptic stimulators of sympathetic receptors. They are dihydroxyphenylethlalamine structures (don’t need to know), fairly polar, and degraded by COMT.

Question 2

List the Natural Catecholamines.

Answer 2

1. Epinephrine
2. Norepinephrine
3. Dopamine

Question 3

What is the MOA of Epinephrine?

Answer 3

1. Epinephrine works on the β 1,2 > α 1,2 receptors.
2. Physiological release from adrenal medulla → blood volume redistribution
3. β2 - vasodilation in muscle, brain, heart; bronchodilation; glycogenolysis
4. α1 - vasoconstriction in skin, GI, kidney
5. In medical dose (higher) → BP ↑ (α effects) and HR ↑ (β1)

Question 4

What is the route of administration of Epinephrine?

Answer 4

1. usually IM or SC injection (orally neutralized by gastric HCl)
2. doesn’t cross BBB

Question 5

What are the indications of epinephrine?

Answer 5

1. Anaphylactic shock (antagonizes histamine effect)
2. Asthma attack (not chronic treatment though, maybe only in severe attack)
3. Surgical vasoconstriction: ↓ absorption of local anesthetics
4. Cardiac arrest as intracardiac injection
5. Glaucoma - vasoconstriction in ciliary body → ↓ humor

Question 6

What is the MOA of Norepinephrine?

Answer 6

Norepinephrine works on the α1,2 > β1 >>> β2.

Question 7

What are the kinetics like for Norepinephrine?

Answer 7

1. parenteral admin (IV)
2. lasts 2-3 minutes (maybe given as infusion)
3. Rapidly metabolized.

Question 8

What can be some adverse effects of norepinephrine administration?

Answer 8

1. Don’t administer in peripheral veins (if possible) due to strong vasoconstrictive effect. Effect is mostly vasoconstrictive (*strongest pressor available*) + ↑ contractility
2. Rise in blood pressure will cause reflex bradycardia. by comparison, epinephrine will increase the heart rate (this sort of thing often asked on exams)

Question 9

What are the indications of norepinephrine?

Answer 9

neurogenic, septic and cardiogenic shock

Question 10

What is the MOA of Dopamine?

Answer 10

Dopamine works on the D > β1 > α1.

Question 11

What are the indications of Dopamine?

Answer 11

1. Low dose: 0.5-2.5 microgram/kg/min. acts on D1 receptors. Good for shock kidney - dilates renal vessels.
2. Medium dose: 2.5-5 microgram/kg/min. acts on β1 receptors. Good for acute heart failure and chronic congestive heart failure in decompensated state. Also cardiogenic shock.
3. High dose: 5-10 microgram/kg/min. agonist on α1 receptors. Can be used as a vasoconstrictor.

Question 12

What are the complications of dopamine?

Answer 12

1. Tolerance develops via receptor downregulation
2. Causes tachycardia (used only when strictly necessary)

Question 13

List the Synthetic catecholamines.

Answer 13

1. Dobutamine
2. Isoprenaline

Question 14

What is the MOA of Dobutamine?

Answer 14

Dobutamine is a selective β1 agonist (slight β2 activity).

Question 15

What are the indications of Dobutamine?

Answer 15

Similar indications to dopamine, but more commonly used

1. AHF
2. CHF
3. cardiogenic shock
4. pharmacological stress testing

Question 16

What are the complications of Dobutamine?

Answer 16

Same complications as DA

Question 17

What is the MOA of Isoprenaline?

Answer 17

1. Isoprenaline (AKA isoproterenol) is a non-selective β1/2
2. not used medically anymore,
3. was precursor structure to current β2 agonists + β blockers