Inotropic Agents

Question 1

Indications for digitalis

Answer 1

CHF Atrial arrythmias

Question 2

MOA digitalis

Answer 2

Inhibits Na/Ka ATPase

• Increase intracellular [Na]
• • Na exchanged for Ca via Na/Ca exchange*
• • Increased intracellular [Ca] —-> positive inotrope*

Question 3

What effects does Digitalis have on: HR, conduction, contractibility, extiability, diuresis, and aqueous humor/CSF

Answer 3

HR: decreased

Conduction through AV: decreased

Contractability: increased (more Ca)

Excitability: increased (decrease K+ in cells)

Diuresis: increase (increased renal blod flow and GFR, decreased aldosterone)

Aqueous humor/CSF: decreased

Question 4

Adverse effect of Digoxin in dogs

Answer 4

Vomiting (stimulates chemotrigger zone)

Question 5

Oral bioavailability of Digoxin

Answer 5

High in elixir forms

Lower in horses

Very low in ruminants (microflora)

Question 6

What is dose of Digoxin based on *

Answer 6

Lean body weight *

Question 7

Distribution of digoxin

Answer 7

Plasma proteins –> wide distribution

• Poor distribution in fat

Enterohepatic circulation

Question 8

Excretion of Digoxin

Answer 8

Renal

Question 9

Is Digitalis effective for ventricular arrythmias

Answer 9

No - only atrial arrythmias

Can cause ventricular arrythmias due to slow AV conduction

Question 10

Dosings of digitalis

Answer 10

1. LOADING DOSE (digitalization –> based on lean body weight)
2. Slow methd –> mild cardiac failure. 5 dose/48h
3. Rapid metod –> 3 dose/6hr
4. Intensive –> emergencies. 1/2 dose, then 1/4 dose 6hours later and then 1/8 dose

Question 11

T/F Digitalis is routinely used in cats

Answer 11

THEY ARE SENSITIVE! Only in emergencies

Question 12

T/F Digitalis has a narrow safety margin

Answer 12

True

Question 13

When monitoring Digitalis toxicity you need to routinely check serum K+ and Ca+. Why?

Answer 13

Potassium

Digitalis competes for a binding spot with K+

Hypokalemia = less K = increased binding sites for Digitalis —-> toxicity

Calcium

Hyper calcemia –> increased Ca for contraction –> increased toxicity

Question 14

What can you give for Digitalis toxicity

Answer 14

1. K+
2. Cholestyramine
3. Atropine

Question 15

Important drug interaction with Digoxin

Answer 15

Quinidine: displaces Digoxin from tissues, increasing concentration 2x –> toxicity

Decrease Digoxin dose 6-8 days before giving Qunidine

Question 16

T/F - Digoxin dose should be reduced in patients with kidney and liver disease

Answer 16

True

Question 17

T/F Parenteral is a preferred route of administering Digitalis

Answer 17

False - it is irritating

Question 18

Two important effects of diuretics

Answer 18

1) Reduce edema
2) Reduce preload

Question 19

How do loop diuretics work? Give an example

Answer 19

Furosemide

• Act on luminal membrane of ascending loop of Henle
• Inhibits Na/K/Cl co-transport –> increased excretion
• Also interferes with Mg and Ca resorption (due to reduction in transcellular voltage different)

Question 20

MOA of Thiazide diuretics

Answer 20

1. Inhibit Na/Cl symporter in DT
2. Na exchanged for K in CD –> hypokalemia
3. Increased Ca resorption

Question 21

Which type of diuretic is slow onset

Answer 21

Potassium sparing diruetics

Question 22

What’s an aldosterone antagonist

Answer 22

Spirinolactone

Question 23

What are two Na-resoprtion inhibitors (potassium sparing diuretic)

Answer 23

1. Triamterence

2. Amiloride

Question 24

What’s a desirable combo with Spirinolactone

Answer 24

Hydroflumethiazide

Question 25

What can diuretics be given with to reduce edema

Answer 25

Digoxin

Question 26

Phosphodiesterase inhibitors

Answer 26

* Inamrinome / Milrinone * Pimobendan * Aminophylline

Question 27

MOA phosphodiesterase inhibitors

Answer 27

Selective inhibition of phosphodiesterase isoenzyme III (degrades cAMP. More cAMP = more contraction and vasodilaton)

Question 28

Which durg produces positive inotropic action without increasing myocardial O2 consumption

Answer 28

**Inamrinone** ## Footnote **Pimobendan**

Question 29

Administration Inamrinome

Answer 29

IV

Question 30

Indications Inamrinome

Answer 30

Acute myocardial failure in dogs/cats

Question 31

Side effects Inamrinome

Answer 31

Tachycardia (humans)

Question 32

T/F phosphodiesterase inhibitors have positive inotropic effect without increasing myocardial O2 consumption

Answer 32

True!

Question 33

Which phosphodiesterase inhibitor is considered a safer alternative to Digitalis

Answer 33

Pimobendan ## Footnote * No effect on oxygen demand* * No arrythmia effects*

Question 34

Whats a B1 agonist used for its inotropic effects in acute conditions

Answer 34

Dobutamine

Question 35

Side effects Dobutamine

Answer 35

Arrythmias (with ischemic heart conditions) Tachyphylaxis (chronic use)

Question 36

T/F Dobutamine has short half life

Answer 36

Yes -- requires *continuous IV administration*

Question 37

Indications for Dobutamine in dogs and horses

Answer 37

**Dogs** * Dilated cardiomyopathy due to CHF * Cardiogenic shock (alternative to dopamine) **Horses** * Hypotension during anesthesia

Question 38

MOA Aminophylline

Answer 38

Phosphodiesterase inhibitor (increased cAMP)

Question 39

Therapeutic uses Aminophylline

Answer 39

Acute pulmonary edema in CHF

Question 40

Primary effect aminophylline

Answer 40

Bronchodilation (also weak inotrope, mild diuresis) *Used for acute pulmonary edema in CHF*