What are the major classes of Inotropic Drugs?
Cardiac Glycosides, Phosphodiesterase inhibitors, beta-1 agonist, Aminophylline
Cardiac glycosides consist of what drugs?
Digoxin + Digitoxin +Oubian → Digitalis glycosides
Inhibits Na/K ATPase → exchange of Na for Ca → increased Ca in contractile proteins → positive inotropic action
Effects of Digitalis?
Increase vagal tone → decrease in SA node activity → decrease in heart rate. Decreased Av node conduction. Diuretic response → decreased edema
Digitalization accomplishes what?
loading and maintenance dose → get effect with small amount of drug.
What do you base the dose of digitalis on?
Lean body weight (not well absorbed by fat)
Vd for digitalis?
dependent on K and Ca serum electrolytes low serum potassium increases digitalis toxicity
Tx for Digitalis Toxicity?
Mild – give oral potassium supplement. Quinidine → displaces digoxin from binding site and inhibits PgP
What can improve the inotropic action as well as vasodilation?
What are the 3 Phosphodiesterase inhibitors?
Milrinone, Amrinone, and Pimobendan
MOA of Dobutamine?
Selective beta-1 agonist
MOA of aminophylline?
SE of Aminophylline?
What is Aminophylline used to Tx?
Causes Diuresis which relieves pulmonary edema brought on by CHF
What diuretics can be utilized as anti-edema drugs?
Thiazides (K excretion increased) and K sparing diuretics (Spioronolactone, triametrene and amiloride)
List the main vasodilators
Sodium Nitroprusside, Prazosin, Nitroglycerin, isoxsuprine, Amlodipine, Hydralazine/Minoxidil
MOA of Prazosin
alpha1 antagonist (→ renin release)
Increased NO release → improves cGMP release
Calcium channel blocker
What do you use Amlodipine for?
Tx for hypertension in cats
What class of drugs is good to use in ischemic heart Dz?
Ace Inhibitors: they produce vasodilation without inducing the sympathetic activation = safer for ischemic heart disease.
What are the main indications for Ace inhibitors?
Heart failure and hypertension
What is the significance of Ace inhibitors?
Produce vasodilation without inducing sympathetic activation
PDE3 Ace inhibitor drugs?
Captopril. Prodrugs: Enalapril, Benazepril
PDE5 Ace Inhibitors?
Sildenafil – used for hypertension in dogs
Why combine Ace inhibitors with Thiazides?
Thiazides → loss of K. Ace inhibitors → K sparing
Interaction of NSAIDs with Ace inhibitors?
NSAIDs decrease hypotensive effect of Ace by blocking bradykinin induced vasodilation (PGI2 mediated)
What should you never use with epinephrine?
Left ventricular failure drugs: Morphine sulfphate
What does morphine sulphate block?
Medullary respiratory center
Never combine what two anti-arrhythmia drugs?
Calcium channel blocker and beta-blockers
Class I MOA
Causes blockade of voltage gated Na+ channels. Reduces max rate of depolarization in cardiac fibers (phase 0 ) without affecting resting membrane potential. Local anesthetics for nerves and myocardial cell membrane.
Effects of class I drugs
Increase the threshold of excitability. Decrease the conduction velocity. Prolongs the effective refractory period. → controls arrhythmia via inhibition of spotaneous depolarization. Also local anesthetics for nerves and myocardial cell membrane.
Class I A specific effects
depress phase 0 of AP: prolong the duration of action potential and refractory period in normal and injured cardiac cells
Class I A drugs?
Quinidine, Procainamide, (disopryramide)
Why do you have to increase digitalis when giving it with quinidine?
Quinidine displaces digitalis from binding site
Class I B specific effects
Decrease phase 0 depolarization and conduction velocity in injured cardiac cells. Min effect on AP/refractoy period
Class I B Drugs
Phenytoin – tx arrhythmia,
Apridine – broad spectrum
SE of Apridine?
Class II MOA
beta adrenoceptor antagonist: beta blockers
Class II effect
Shortens AP and refractory periods
Class II drugs
Propranolol is indicated for what kind of arrhythmia?
Catecholamine induced/ halogenated hydrocarbon arrhythmias