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Cardiodrug
| Question | Answer |
|---|---|
| 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 |
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alljacks
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