Thursday September 23, 2010
(1) Dobutamine = B1 agonist (minor B2 and α1 agonist)
Inotropic (↑SV and ↑ contractility) but not chronotropic (does not ↑ HR)
Used to treat heart failure by ↑CO
**since it does not activate D receptors (which release norepinephrine) Dobutamine is is less prone to induce hypertension
Mnemonic: Dobutamine sounds like Dopamine. So when you see a patient with Cardiac Failure think of using Dopamine BUT without the bad D receptor effects.
(2) Phenylephrine = α1 agonist (minor α2 agonist)
Used clinically:
nasal decongestant (nasal spray or PO)
pupil dilation (for eye exams)
Vasoconstrictor
To ↑ BP for pts with hyp0tension
To abort priapsism (nonsexual erection)
Side effects = Hypertension
This mnemonic is very much like a MMRS
First of all you see the word EPHRINE in the word so you know that the drug has “epinephrine-like” properties.
Now look at the picture below:
This man who has phenyl groups for eyes has an unwanted erection and a runny nose. He is so embarrassed that he is hypOtensive.
After you prescribe Phenylephrine, he feels so much better that his eyes brighten (mydriasis)
Clarification:
ReplyDeleteDopamine itself stimulates Beta receptor and Dopamine receptors. It can be used for Shock pts because you want to increase the rate and the strength of the Heart Beat as well as prevent kidney failure.
Dopamine receptors cause vasodilationin the renal arteries and other major organs (brain, lungs). So for Hypertensive Emergencies D1 agonists are great (Fenoldopam).
Dobutamine is a B1 agonist that causes and increase in contractility of heart and an increase in HR. During Acute Heart Failure the BP is low! You do NOT want to stimulate urinary excretion.
Nice post!
ReplyDeleteAs high doses, dopamine can even stimulate alpha receptors, thus it would not be good for shock at high doses. The increased vasoconstriction would promote hypoxia. Also, this vasoconstriction can illicit reflex bradycardia. A low cardiac output with peripheral vasoconstriction is life threatening! In there's an accidental overdose, you need to give an alpha-1 blocker.
You had it right in the first post Lindsey. Dobutamine does not increase HR! It has ionotropic action, but not chronotopic.
All that foundational ANS stuff is coming back to haunt us. Good call Dana on reviewing this stuff!