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Cardiodrug

QuestionAnswer
Drugs that generally increase myocardial contractile force and are indicated for congestive heart failure conditions (CHF).
in inadequate output and insufficient delivery of oxygen to the meet the tissue requirements CHF
collectively termed Digitalis digoxin,digitoxin,ouabain
MoA: inhibition of Na+/K+ - ATPase enzyme Cardiac glycosides
Cardiac glycosides improved myocardial contractility, increased cardiac output (CO), diuresis, control of arrhythmias, reduction in blood volume, venous pressure, heart size and heart rate (HR).
Decreases HR: stimulation of vagal tone and depression of SA node conduction Effects of cardiac glycosides
Anti-adrenergic action at the AV-junction: AV conduction is decreased effects of cardiac glycosides
Positive inotropic action on the heart: increases ventricular contraction strength Effects of cardiac glycosides
does not induce diuresis if edema is not cardiogenic Digitalis
Diuretic response to digitalis secondary to circulatory improvement
dogs undergoing therapy with oral digitalis preparations is suggestive of digitalis toxicity Vomiting accompanied by diarrhea
is not well distributed into fat digitalis
dosed based on lean body weight. digitalis
This drug is not suitable for ruminants due the poor absorption digitalis
CHF (primary) Therapeutic indications of digitalis
Atrial arrhythmias (secondary) Therapeutic indications of digitalis
involves the administration of a large amount of digitalis (loading dose) in several doses over a relatively short period (24-48 hours) to achieve a rapid therapeutic effect. Digitalization
The main aim of therapy with digitalis is to determine the smallest amount of glycoside that will effectively maintain the patient in a state of cardiac compensation without inducing signs of intoxication
loading dose is 25mg/kg, given at 12 hour intervals for 36 hours (4 doses total). Slow method (mild cardiac failure)
Loading dose is administered as 22mg/kg at 6 hour intervals, for a total of 3 doses on the first day of treatment Rapid method
one-half of the loading dose is given initially; one fourth is given 6 hours later, and one eighth is given at 4-6 hour intervals Intensive method (for emergency situations)
11mg/kg is given at 12 hour intervals After initial digitalization is achieved, the daily maintenance dose of digoxin
6th to 8th day of maintenance therapy (preferred period) Steady-state concentration will be attained
not commonly used in cats digitalis
dose levels should be reduced in animals with liver or kidney disease digitalis
IV administration of digitalis is indicated when the animal does not retain oral medications or has acute cardiac decompensation or respiratory distress
causes pain and swelling at injection site, therefore this route is not preferred IM administration of digitalis
has a narrow range of safety Digoxin
Therapeutic plasma concentration is in range of 0.6-2.4ng/ml Digoxin
vary from mild GI disturbances to protracted diarrhea, chronic weight loss, arrhythmias, and exercise intolerance digitalis toxicity
is affected by the availability of K+ and Ca2 cardiac toxicity of digitalis
potentiates arrhythmogenicity Hypokalemia
antagonizes arrythmogenic potential hyperkalemia
antiarrhythmic activity of K+ in digitalis intoxication is due to the inhibition of cardiac glycoside binding to Na+,K+-ATPase enzyme
First, isolate the animal and keep him/her quiet to reduce excitability. Treatment of digitalis toxicity
Oral potassium administration Treatment of digitalis toxicity
Cholestyramine resin to bind glycoside w/in the GI, hastening elimination Treatment of digitalis toxicity
Anti-arrhythmic agents (lidocaine, propranolol, phenytoin) Treatment of digitalis toxicity
Atropine may be useful in cases with bradycardia Treatment of digitalis toxicity
act on the thick ascending limb (TAL) of the loop of Henle Loop acting diuretics
furosemide Loop acting diuretics
act on the distal convoluted tubule (DCT) Thiazide diuretics
higher K+ excretion and enhances Ca2+ resorption Thiazide diuretics
Due to these effects, the toxic potential of digitalis increases higher K+ excretion and enhances Ca2+ resorption
work on the renal collecting tubules Potassium sparing diuretics
inhibiting resorption of Na slow onset of action Potassium sparing diuretics
When using diuretics to treat CHF consider and monitor serum K+ levels
produces diuresis without either delayed onset of action or excessive urinary excretion of K An oral combination preparation containing hydroflumethiazide (thiazide diuretic) and spironolactone (K+ sparing diuretic) in equal proportion
The objectives of digoxin therapy are to reduce the ventricular rate by slowing AV conduction and improving the cardiac efficiency
The administration of quinidine to horses or dogs on maintenance therapy with digoxin increases the average steady-state plasma digoxin concentration approximately two-fold.
The basis of quinidine-digoxin interaction is a decreased volume of distribution of digoxin due to its displacement by quinidine from tissue binding sites
the maintenance dose of digoxin should be halved 6-8 days prior to therapy with quinidine
Other positive inotropic agents Phosphodiesterase inhibitors
Referred to as nonglycoside, noncatecholamine inotropic drugs Phosphodiesterase inhibitors
Amrinone Phosphodiesterase inhibitors
Milrinone Phosphodiesterase inhibitors
Bipyridine Phosphodiesterase inhibitors
Inhibit phosphodiesterase isoenzyme III resulting in an intracellular accumulation of cAMP àproduces a positive inotropic effect and peripheral vasodilation without consuming O2 Amrinone, Milrinone, Bipyridine
Indicated for the treatment of acute myocardial failure Amrinone, Milrinone, Bipyridine
b-adrenergic agonists Dobutamine
Dobutamine A direct b1-agonist à increases CO and decreases ventricular filling pressure
Arrhythmias,Tachyphylaxis,Increases myocardial O2 demand b-adrenergic agonists: Dobutamine drawbacks
b-adrenergic agonists clinical indications Acute treatment of dilated cardio myopathy ass w/ CHF, alternative in cardiogenic shock condtions, Management of hypotension during anesthesia in horses
Dobutamine has a short half life (2-4) due to rapid biotransformation by O-methyltransferase
drug requires continuous administration Dobutamine
Produces chronotropic and weak inotropic action on the heart; due to inhibition of phosphodiesterase enzyme in the heart Aminophylline
principal effect is bronchodilation Aminophylline
it is useful for the treatment of acute pulmonary edema Aminophylline
it is NOT indicated for management of CHF Aminophylline
These drugs relax and dilate smooth muscle of arterioles, thereby reducing systemic vascular resistance VASODILATORS
can selectively dilate arteries, veins or have activity of both balance dilators
decrease systemic vascular resistance which decreases afterload Arteriolar dilators
A reduction in afterload decreases myocardial O2 demand and increases CO.
diverts blood volume from pulmonary circulation to systemic circulation Peripheral venodilation
The primary benefit of this is reduction of preload and decreased edema formation Peripheral venodilation
VASODILATORS drawbacks Does not increase peripheral perfusion and oxygen availability to all tissues (ex. Nitroglycerine)
Reflex tachycardia due to vasodilation increases myocardial O­2 demand VASODILATORS drawbacks
A balance dilator; most efficient vasodilator used in hypertensive emergencies in human patients Sodium nitroprusside
Hydralazine and Minoxidil Arteriolar vasodilators
These drugs are most beneficial for treating CHF that is secondary to mitral valve insufficiency/aortic valvular insufficiency Hydralazine and Minoxidil
Arteriolar vasodilators reduces peripheral vascular resistance mainly by the opening of potassium channels in arteriolar smooth muscle
concentrations will be higher in uremic patients Plasma hydralazine
Side effects: Tachycardia Hydralazine and Minoxidil
A selective a1-adrenergig blocking agent,produces vasodilation with minimal reflex tachycardia,better for treating CHF Prazosin
Balance dilator with NO effect on cardiac or skeletal muscle,it has a rapid onset of action (1-3 minutes) Nitroglycerine
It is the drug of choice given by sublingual route for treatment of angina. Nitroglycerine
The oral bioavailability of the drug is < 1% due to a first pass effect. Nitroglycerine
The commercial veterinary preparation of nitroglycerine is a 2% topical ointment for dogs (cardiogenic pulmonary edema) and horses (acute laminitis) Nitroglycerine
Non-sel b-adren agonist,prod vasodilation of skel mus vasculature & relax of uterine sm mus by b2-adrceptors & prod + inotropic action on heart by b1-adrceptors Isoxsuprine
Isoxsuprine clinical indications To relieve parturition complication,Navicular disease in horses
is a powerful vasoconstrictor Angiotensin II
are commonly used drugs to treat heart failure and hypertension ACE inhibitors
They produce vasodilation without significantly effecting the heart ACE inhibitors
do not activate the sympathetic system, so they can safely be used in ischemic disease ACE inhibitors
Enalapril maleate,Benazepril hydrochloride,Catopril ACE inhibitors used in veterinary medicine
Isolated from the venom of a pit viper,Bioavailability reduced when administered with food Catopril
Prodrugs,Bioavailability NOT affected by food Enalapril maleate and Benazepril hydrochloride
ACE inhibitors act by Inhibiting the enzyme peptidyl dipeptidase which hydrolyzes angiotensin I to angiotensin II,Inhibition of bradykinin degradation
ACE inhibitors are eliminated by renal excretion so monitor renal function in patients on these drugs
is an alternative to digoxin in the treatment of mild CHF in dogs and cats Enalapril
Prior to therapy with enalapril diuretics should be given. Furosemide at 2mg/kg should be administered orally, once daily for 2-4 days
There are 3 main aims to the treatment of acute left ventricular failure, which is characterized by pulmonary edema
3 main aims to the treatment of acute left ventricular failure Improve gas exchange,Enhance myocardial contractility (infuse dobutamine to effect),Reduce wrkload of lftvtr (admin loop acting diuretic furosemide IV)
Primary effect = increases venous capacitance by redistributing blood from the lungs toward the peripheral circulation thus alleviating pulmonary congestion Furosemide
Hypotensive effect & decr response of medullary resp center due to incr part press of CO2,it relieves dyspnea & anxiety ass w/ lftvent failure Morphine sulphate
is contra-indicated in acute left ventricular failure due to its peripheral vasoconstriction and arrhythmogenic activity Epinephrine
ANTI-ARRHYTHMIC DRUGS Aim of therapy Reduce ectopic pacemaker activity, Regularize the conduction pathway
membrane stabilizers/local anesthetics Class I
b-adrenergic antagonists Class II
agents that prolong the refractory period Class III
calcium channel blockers Class IV
these drugs depress the rate of influx through fast Na+ channels and thus decrease the maximal rate of depolarization Class I anti-arrhythmic drugs
Class IA anti-arrhythmic drugs Quinidine
Class IA anti-arrhythmic drugs Procainamide
Class IA anti-arrhythmic drugs Disopyramide
Class IA anti-arrhythmic drugs Prolong the cardiac action potential during the refractory period
Class IB anti-arrhythmic drugs Lidocaine
Class IB anti-arrhythmic drugs Phenytoin
Class IB anti-arrhythmic drugs Tocainide
Class IB anti-arrhythmic drugs Mexiletine
Class IB anti-arrhythmic drugs Aprinidine
Class IB anti-arrhythmic drugs Produce minimal shortening effect on the action potential during the refractory period
Class IC anti-arrhythmic drugs Encainide
Class IC anti-arrhythmic drugs Lorcainide
Class IC anti-arrhythmic drugs Flecainide
Class IC anti-arrhythmic drugs Reduces the maximal rate of phase 0 depolarization in normal as well as abnormal cardiac cells, but exerts a small effect on refractoriness and action potential
Class II anti-arrhythmic drugs Propranolol (prototype)
Class II anti-arrhythmic drugs Oxyprenolol
Class II anti-arrhythmic drugs Alprenolol
Class II anti-arrhythmic drugs Metoprolol
Class II anti-arrhythmic drugs Timolol
Class II anti-arrhythmic drugs Pindolol
Class II anti-arrhythmic drugs b-blockers; depress automaticity, prolong AV conduction and decrease HR and contractility (negative chronotropic and inotropic effects); also shorten the duration of action potentia
Class III anti-arrhythmic drugs Bretylium
Class III anti-arrhythmic drugs Amiodarone
Class III anti-arrhythmic drugs Pure, prolongation of the action potential, thereby extending the action potential
Class IV anti-arrhythmic drugs Verapamil
Class IV anti-arrhythmic drugs Dilitiazem
Class IV anti-arrhythmic drugs Calcium channel blockers à slow AV conduction.
Class IV anti-arrhythmic drugs These drugs must be given with extreme caution to patients that are receiving b-blocker therapy because the co-administration of these drugs could predispose the patient to AV block
Class IV anti-arrhythmic drugs clinical uses Supraventricular tachyarrhythmias and ventricular hypertrophy in dogs and cats
Class IV anti-arrhythmic drugs side effects Hypotension and bradycardia
only for the initial phase; used for treating atrial arrhythmias Digitalis glycosides
Classified as a Class IA agent Quinidine sulphate
It exerts an atropine-like vagolytic effect and therefore antagonizes the cardiac actions of vagally released Ach, thus effectively controls atrial tachyrrhythmias Quinidine sulphate
Directly to prolong the refractory period Quinidine
Indirectly lengthens refractory period by its anti-cholinergic action Quinidine
The vagolytic activity of induces improved AV conduction Quinidine
Contraindications: not recommended in AV block or interventricular block Quinidine
Pharmacological action is similar to quinidine Procainamide hydrochlorate:
is more effective in controlling ventricular arrhythmias than atrial arrhythmias Procainamide hydrochlorate:
Class IB drug with pharmacologic action similar to quinidine Phenytoin sodium
is considered effective in controlling digitalis-induced arrhythmias and for treatment of ventricular arrhythmias. Phenytoin sodium
Dogs receiving phenytoin tend to develop phenytoin toxicosis when is given during the therapeutic regimen, since it inhibits the metabolism of phenytoin chloramphenical
Postural ataxia,Hypermetric gait Phenytoin sodium Signs of toxicosis
Class IB drug,local anesthetic w/ antiarrhythmic action effective for treatment of ventricular tachyarrhythmias Lidocaine hydrochloride
Has a rapid onset and short duration of action,this combined w/ the fact this drug has inefficient absorp after PO admin make this a poor drug for maintenance therapy Lidocaine hydrochloride
Dose,IV:2-4mg/kg as a bolus over 1-2 minutes,0.5-2.0mg/kg, every 20-60 minutes,Slow injection:25-60ug/kg/min,Constant infusion while monitoring Lidocaine hydrochloride
b-blocker prototype, effective in controlling cardiac arrhythmias due to sympathetic over activity Propranolol hydrochloride
Cardioselective b1-blocking agent Metoprolol tartrate
Drug of choice for in patients with history of chronic obstructive airway disease Metoprolol tartrate
Class IV drug, calcium channel blocker Verapamil and Dilitiazem
Decreased contractile response of the heart,Reduced CO,Hypotension Adverse effects of calcium channel blockers
are used cautiously in cardiac failure patients Calcium channel blockers
Class III drug Bretylium
Admin of to animals anesth w/ holgenated hydrocarbon anesth is contradicated, b/c these anesth sensitize myocardium to arrhythmogenic activities of catecholamines Bretylium
Class III drug Amiodarone
Long biologic half life,requires days to weeks to reach steady state Amiodarone
Class IA drug Disopyramide
Class IB drug; it is a structural congener of lidocaine and possesses similar activity Tocainide
Advantages:It is effective after oral administration,It possesses a long duration of action Tocainide
It can be used as a substitute for lidocaine Tocainide
Class IB drug; similar actions as lidocaine and tocainide Mexiletine
Dose:1-2mg/kg, orally 2-3 times daily Mexiletine
Class IB drug Aprindine
Side effects:Leukopenia,agranulocytosis,hepatotoxicosis,Hypotension,ataxia,nausea,seizures,depression of myocardial contractile response & prolong PR,QRS,QT intervals Aprindine
This drug is used as a last resort when all other treatments have failed due to drug resistance Aprindine
Class IC drug:block Na conductance but does not cause a prolongation of the refractory period Encainide, Flecainide and Lorcainide
is mix(a1,b1,b2)adrceptor agonist & potent vasopressor,exert+inotropic&chronotropic on heart(b1)&vasocon in vasc beds(a)also cause vasodilation(b2)in skel mus vasculature EPINEPHRINE
EPINEPHRINE clinical indications Acute allergic & anaphylactic rx,Cardiac arrest,Prolongs effects of local anesthetics
EPINEPHRINE contraindications Acute left ventricular failure,Cardiac emergencies during anesthesia
It is a non-selectivebb-adrenoceptor agonist,increases CO ISOPROTERENOL
Short-term emergency management of partial or complete heart block,Cardiac arrest ISOPROTERENOL clinical indications
Different effects at different doses DOPAMINE
DOPAMINE Low rate of IV infusion Vasodilation especially in renal and splanchnic artery beds
DOPAMINE Intermediate rate of IV infusion Stimulates b1-adrenoceptors in heart prod a +inotropic action & decreased peripheral vascular resistance
Dopamine clinical indications Increased CO increases GFR, thus can be given as adjunctive therapy for oliguric renal failure
In severe hypotension (cardiogenic shock) can be used for support in adequate plasma replacement dopamine
Created by: alljacks