Cardiac Glycosides and Inodilators Flashcards
What two clinical conditions in veterinary practice would you use cardiac glycoside for treatment
dilated cardiomyopathy and endocardiosis
What symptoms are shown with Class 1 congestive heart failure?
only strenous exercise is limited
What symptoms are shown with Class 2 congestive heart failure?
fatigue, shortness of breath, coughing on exercise
What symptoms are shown with Class 3 congestive heart failure?
comfortable at rest but excercise is minimal
What symptoms are shown with Class 4 congestive heart failure?
no capacity for exercise, clinical signs at rest
What drugs can be used for class 2-4 congestive heart failure?
digoxin, pimobendan, ACE inhibitors, and other inotropic drugs
What is the goal of drugs used to treat congestive heart failure?
the goal is to increase stroke volume
What is the problem with digoxin?
getting the dose right
What form of digoxin is the best use?
in a liquid form
What is the mode of action of glycoside?
Glycoside → inhibition of Na/K exchange → Increased Na concentration → decreased Na/Ca exchange → Increased Ca concentration → increased contraction and rate
What are the major actions of cardiac glycosides?
Positive inotropic action - increased force
Negative chronotropic effect - slowing of the heart
Negative dromotropic effect - slowing conduction of the AV node
How do cardiac glycosides create a negative chronotropic effect?
they stimulate the vagus nerve and also improve baroreceptor sensitivity countering sympathetics
What is the half-life and elimination method of digoxin in dogs?
Half-life - 23-39 hours
Elimination - mainly renal
What is the half-life and elimination method of digoxin in cats?
Half-life - 25-78 hours
Elimination - renal
What is the half life and steady state of digoxin in horses?
Half-life - 13-23 hours
Elimination - renal
What are the deleterious effcts of digoxin on the heart rhythm and GI tract?
Auricular arrhythmias/tachycardia
AV block
Ventricular arrhythmias/extra-systole/pulses bigemiini/Ventricular fibrillation
Gi disturbances - anorexia, vomiting, diarrhea
Generally how do you treat digoxin toxicity?
stop giving the drug and allow it to be cleared and give IV fluids to maximize renal clearance
How do you treat ventricular arrhythmias due to digoxin?
treat with lidocaine, phenytoin, and propanolol
What inodilator did we discuss in class?
Pimobendan (vetmedin)
What is the general action of inodilators?
Ca sensitizer and phosphodiesterase III inhibitor
How does calcium sensitization work?
Normally, troponin I inhibits actin and myosin combination until calcium binds to troponin C. Calcium sensitizers increases binding calcium to troponin C
How does phosphodiesterase III inhibition work?
it prevents cAMP breakdown and increases PKA action and increases voltage-activated calcium currents
What are the therapeutic responses to glycosides and pimobendan?
Increase cardiac output
Decrease in heart rate
Decrease in venous pressure
Reduced heart size
Water loss and reduced body weight
In the heart, what does dopamine act on?
D5 receptors in the heart to increase cAMP
What is dobutamine and what is it useful in treating?
It is a Beta-1 agonist - it is useful I/V with acute reversible heart failure
What is amrinone and what is it useful for?
It is a phosphodiesterase III inhibitor useful in I/V to increase cAMP which increases Ca influx
