Inotropes and Vasopressors

Question 1

How is Digoxin a:
- positve inotrope
- negative chronotrope

Answer 1

• inhibits Na/K pump, increasing intracellular sodium = more available for calcium exchange = increased contractility
• decreases AV node conduction by enhancing vagal tone

Question 2

How is Digoxin a(n):
- pro-arrhythmic drug
- anti-arrhythmic drug

Answer 2

Pro: if accumulated to toxic levels (ie., administered to hypokalemic patient –> fewer chances of there being non digoxin-bound Na/K pumps that can dilute out the effects of those that are digoxin-bound), can lead to arrhythmias

Anti: as adjunctive tx of supraventricular arrhythmias (e.g., slow down HR in A-fib)

toxic levels are common and can be lethal, cats > dogs

Question 3

Pimobendan MoA

Answer 3

Positive Inotrope
- increases calcium sensitivity in myocardiocytes
- inhibits PDE3 -> increased contractility / vasodilation effects

venous vasodilation -> reduces preload, which minimizes congestion in tissues

arterial vasodilation –> reduces afterload, which eases cardiac workload and increases tissue perfsusion

Question 4

What drugs enhance digoxin toxicity via increasing its serum levels?

Answer 4

Furosemide and Quinidine

furosemide decreases potassium levels in blood

Question 5

Clinical uses of pimobendan

Answer 5

tx of CHF 2º to…

DOGS: MMVD or DM

CATS: end-stage HCM, or DCM

Question 6

what triple therapy is commonly used for CHF?

Answer 6

Furosemide + Enalapril + Pimobendan (+/- spironolactone)

no single drug is effective enough on its own for tx of CHF!!

Question 7

Uses of vasopressors

Answer 7

ER tx of severe hypotension, cardiopulmonary shock; anesthesis

Epinephrine, Dopamine, Dobutamine

Question 8

MoA of Epinephrine

Answer 8

Adrenergic agonist:
1. Alpha1 = vasoconstriction of smooth muscle (vessels)
2. Beta1 = positive inotrope and chronotrope
3. Mild Beta2 = bronchodilation

Question 9

Why is epinephrine detrimental in CHF patients?

Answer 9

Epinephrine causes greatest increase in myocardial O2 demand (due to great energy usage requirements) –> BAD FOR FAILING HEART!! (CHF already is in low CO//reduced efficiency)

Question 10

Dopamine MoA

Answer 10

endogenous catecholamine with selective B1 activity (positive inotrope & chronotrope), and D receptor (vasodilation)

Question 11

T1/2 of dopamine and dobutamine

Answer 11

2 minutes (always a CRI)

Question 12

Dobutamine MoA

Answer 12

synthetic Beta-1 agonist (mostly a positive inotrope)

Question 13

Vasopressin (ADH) MoA

Answer 13

increases blood pressure by:
- upregulating renal retention of solute-free H2O
- vasoconstriction