Inotropic Agents Flashcards
Indications for digitalis
CHF Atrial arrythmias
MOA digitalis
Inhibits Na/Ka ATPase
- Increase intracellular [Na]
- Na exchanged for Ca via Na/Ca exchange*
- Increased intracellular [Ca] —-> positive inotrope*
What effects does Digitalis have on: HR, conduction, contractibility, extiability, diuresis, and aqueous humor/CSF
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
Adverse effect of Digoxin in dogs
Vomiting (stimulates chemotrigger zone)
Oral bioavailability of Digoxin
High in elixir forms
Lower in horses
Very low in ruminants (microflora)
What is dose of Digoxin based on *
Lean body weight *
Distribution of digoxin
Plasma proteins –> wide distribution
- Poor distribution in fat
Enterohepatic circulation
Excretion of Digoxin
Renal
Is Digitalis effective for ventricular arrythmias
No - only atrial arrythmias
Can cause ventricular arrythmias due to slow AV conduction
Dosings of digitalis
- LOADING DOSE (digitalization –> based on lean body weight)
- Slow methd –> mild cardiac failure. 5 dose/48h
- Rapid metod –> 3 dose/6hr
- Intensive –> emergencies. 1/2 dose, then 1/4 dose 6hours later and then 1/8 dose
T/F Digitalis is routinely used in cats
THEY ARE SENSITIVE! Only in emergencies
T/F Digitalis has a narrow safety margin
True
When monitoring Digitalis toxicity you need to routinely check serum K+ and Ca+. Why?
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
What can you give for Digitalis toxicity
- K+
- Cholestyramine
- Atropine
Important drug interaction with Digoxin
Quinidine: displaces Digoxin from tissues, increasing concentration 2x –> toxicity
Decrease Digoxin dose 6-8 days before giving Qunidine
T/F - Digoxin dose should be reduced in patients with kidney and liver disease
True
T/F Parenteral is a preferred route of administering Digitalis
False - it is irritating
Two important effects of diuretics
1) Reduce edema
2) Reduce preload
How do loop diuretics work? Give an example
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)
MOA of Thiazide diuretics
- Inhibit Na/Cl symporter in DT
- Na exchanged for K in CD –> hypokalemia
- Increased Ca resorption
Which type of diuretic is slow onset
Potassium sparing diruetics
What’s an aldosterone antagonist
Spirinolactone
What are two Na-resoprtion inhibitors (potassium sparing diuretic)
1. Triamterence
2. Amiloride
What’s a desirable combo with Spirinolactone
Hydroflumethiazide
What can diuretics be given with to reduce edema
Digoxin
Phosphodiesterase inhibitors
- Inamrinome / Milrinone
- Pimobendan
- Aminophylline
MOA phosphodiesterase inhibitors
Selective inhibition of phosphodiesterase isoenzyme III
(degrades cAMP. More cAMP = more contraction and vasodilaton)
Which durg produces positive inotropic action without increasing myocardial O2 consumption
Inamrinone
Pimobendan
Administration Inamrinome
IV
Indications Inamrinome
Acute myocardial failure in dogs/cats
Side effects Inamrinome
Tachycardia (humans)
T/F phosphodiesterase inhibitors have positive inotropic effect without increasing myocardial O2 consumption
True!
Which phosphodiesterase inhibitor is considered a safer alternative to Digitalis
Pimobendan
- No effect on oxygen demand*
- No arrythmia effects*
Whats a B1 agonist used for its inotropic effects in acute conditions
Dobutamine
Side effects Dobutamine
Arrythmias (with ischemic heart conditions)
Tachyphylaxis (chronic use)
T/F Dobutamine has short half life
Yes – requires continuous IV administration
Indications for Dobutamine in dogs and horses
Dogs
- Dilated cardiomyopathy due to CHF
- Cardiogenic shock (alternative to dopamine)
Horses
- Hypotension during anesthesia
MOA Aminophylline
Phosphodiesterase inhibitor (increased cAMP)
Therapeutic uses Aminophylline
Acute pulmonary edema in CHF
Primary effect aminophylline
Bronchodilation
(also weak inotrope, mild diuresis)
Used for acute pulmonary edema in CHF
