CARDIOVASCULAR DRUGS

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CARDIOVASCULAR DRUGS

• Chapter

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ANTIARRHYTHMIC DRUGS
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Sodium influx inhibitors

• These drugs decrease the rate of sodium movement
  into the cell
• Allow SA node to regain control of heart rate and
  re-establish sinus rhythm

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Lidocaine

• Only comes in injectable form and is given IV
• MAJOR DRUG OF CHOICE FOR TREATMENT OF VPCS AND
  VENTRICULAR ARRHYTHMIAS
• Caution in cats. AV blocks will worsen. Large
  boluses can produce sinus arrest.
• Signs of toxicity sedation, ataxia, drowsiness,
  excitement, short-lived seizures
• DO NOT USE IV IF BOTTLE ALSO CONTAINS EPINEPHRINE
  (intended for use as a local anesthetic-keep this
  bottle in separate area). Heart rate and
  contractility will increase while sodium movement
  is reduced. Sudden collapse and death is
  possible.
• Mexiletine-Oral drug for long term maintenance on
  dogs who respond to lidocaine

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Quinidine

• Increase length of the refractory period
• PO drug, used for long-term maintenance
• Known to cause GI upset.
• Can cause digoxin toxicity if given
  simultaneously

Procainamide

• Increase length of the refractory period
• PO drug, used for long-term maintenance
• Regular release or sustained-release tablets

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Beta Blockers

• Beta Antagonists. Can block only Beta ones, only
  Beta twos (called selective) or both
  (nonselective).
• Beta blockers decrease sympathetic stimulation of
  the heart, allowing the parasympathetic system to
  control the heart. Conduction of impulses and
  heart rate will slow down.
• Also called Negative Inotropic drugs as the heart
  will contract with less force.
• Will see a prolonged interval between P wave and
  QRS complex (slowed conduction through AV node)
  called 1st Degree AV Block.
• Atropine can reverse Beta blockers if overdose
  occurs.

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Beta Blockers

• Increased numbers of Beta receptors
  (upregulation) may occur if an animal has been
  taking a Beta blocker regularly. This may make it
  difficult for the Beta blockers to be effective,
  so the dose may need to be increased.
• In addition, more receptors makes the tissues
  more sensitive to epinephrine and norepinephrine.
  DO NOT suddenly stop administering Beta blockers
  since a release of epi/norepi by the body will
  result in extreme tachycardia and arrhythmias.
  Slowly taper off of meds to allow the body to
  downregulate its receptors.

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Propranolol

• Prototype for this category
• Blocks Beta one receptors on the SA node and the
  AV node, slowing the speed of the depolarization.
• Used in cats with tachycardia due to
  hyperthyroidism, systemic hypertension, HCM.
• May also block Beta two receptors, causing
  broncoconstriction and vasoconstriction of blood
  vessels to the heart and skeletal muscle.

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• ATENOLOL
• More selective for Beta ones than propranolol.
• Safer to use in animals with bronchospasm.
• Also used with cats that have HCM.
• CARVEDILOL
• Newer med, more selective for Beta one receptors.
• SOTOLOL
• Nonselective for receptors like propranolol.

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Calcium Channel Blockers

• Diltiazem, Verapamil
• Not used as frequently in veterinary medicine as
  the other Antiarrhythmic drugs.
• Block calcium channels which decreases conduction
  of depolarization waves and decreases
  automaticity throughout the heart. Negatively
  effects the contractile mechanism of cardiac
  muscle.
• Negative inotropes
• Amlodipine is used more as a treatment for
  hypertension than arrhythmias.

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POSITIVE INOTROPIC DRUGS

• Increase strength of contraction of weak heart
• Most work by making more Calcium available to the
  contractile proteins of the muscle cell.

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Adrenergic drugs/Sympathomimetics

• Catecholamines are the bodys natural positive
  inotropes that are released when the body is
  stimulated by the sympathetic nervous system.
• Synthetic versions are called adrenergic or
  sympathomimetic drugs.
• Stimulate Beta one receptors in cardiac muscle.
• Improvement in contractility is short-lived.
• Not meant to be long-term drugs.
• Mainly used for short-term treatment of CHF.

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• EPINEPHRINE
• Preferred drug for stimulating contractions post
  cardiac arrest and for anaphylaxis.
• Can be given Intracardiac, Intratracheal, or IV.
• 110,000 solution is preferred. Can be achieved
  by using a 110 dilution of a 11000 solution.
• Store in refrigerator.
•  
• DOPAMINE
• Used for treatment of acute heart failure,
  oliguric renal failure, and treatment of shock.
• Increases blood pressure and cardiac
  contractility.
•  

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Cardiac Glycosides

• Obtained from the dried leaves of the Digitalis
  purpurea (foxglove) plant which improve
  contractility, decrease heart rate, decrease
  arrhythmias, decrease signs of dyspnea.

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Digoxin

•  Makes more calcium available to the contractile
  proteins in cardiac cells.
• Contractions occur with more force, but with a
  decreased rate.
• Dose is often calculated by using the surface
  area of the animal as opposed to the weight.
• Small therapeutic index, so toxicities are
  common. Signs V/D, anorexia, severe bradycardia,
  AV block. STOP MEDS.
• Reverse with Atropine.
• Digoxin has a half-life of up to 50 hours and is
  eliminated via the kidneys. Dehydration will
  prolong the half-life.

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Pimobendan VETMEDIN

• Newer drug
• Increases sensitivity of cardiac myofilaments to
  Calcium
• Used to treat DCM

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VASODILATORS

• Vasoconstriction is a response to decreased
  arterial blood pressure. It results in increased
  resistance to blood flow and increased force to
  push blood through the vessels, making the heart
  work harder.
• Vasodilators decrease resistance to blood flow,
  making it easier for the heart to pump blood
  through the vessels.
• Hypertension unrelated to heart disease is seen
  in hyperthyroidism, chronic renal disease,
  diabetes mellitus, etc. If uncontrolled, retinal
  issues or stroke can occur.
• Vasodilators can work by blocking the
  renin-angiotensin system, directly relaxing the
  smooth muscle in vessel walls, or blocking Alpha
  one receptors. Monitor for weakness, syncope, or
  lethargy when beginning medication.

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Ace Inhibitors

• Animals with CHF have decreased cardiac output
  and decreased blood pressure. Alpha one receptors
  are stimulated so arterioles become
  vasoconstricted.
• Less blood enters the nephron, so less urine is
  made. The renal tubules detect this and release
  RENIN in response.
• Renin converts ANGIOTENSINOGEN to ANGIOTENSIN I.
  Angiotensin I is converted to ANGIOTENSEN II by
  ANGIOTENSINOGEN CONVERTING ENZYME. Angiotensin II
  causing the release of ALDOSTERONE from the
  adrenal glands.
• This causes sodium reabsorption and water
  retention. The end result is increased blood
  volume, pressure, and work load for the heart.

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ACE Inhibitors- Enalapril, Captopril, Lisinopril,
Benazepril

• Block ACE, preventing formation of Angiotensin II
  and Aldosterone.
• Treating with ACE inhibitors is common. Will not
  have an effect on normal animals.
• Also have positive inotropic effect.

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Hydralazine

• Drug of choice before ACE inhibitors were
  invented.
• Directly causes smooth muscle relaxation in
  arterioles. Most likely through Calcium
  inhibition.
• Dilates pulmonary arterioles more than any other
  vessel.
• Slight activity as a positive inotrope.

Prazosin

• Alpha one blocker that causes vasodilation in
  both arteries and veins.
• Give to patients with CHF that are not responding
  to other vasodilators.
• Not used in small animals as it is too hard to
  measure out a small enough dose.
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Nitroglycerin

• Causes venodilation and coronary arteriole
  dilation.
• Well absorbed through skin and mucous membranes.
  Animals use cream or patch. Cream is applied to
  hairless part of pinna. Change site of
  application with each dose. Wear gloves when
  applying and dont pet the animal where the cream
  or patch is applied.
• Improves cardiac output and reduces pulmonary
  edema and ascites.
• No explosions will occur.

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DIURETICS

• Increase urine production and promote water loss.
• Used in the following situations edema/ascites,
  removal of drugs excreted by the kidney, reducing
  arterial blood pressure, decreasing workload on a
  CHF heart
• Use with caution in anyone with hypovolemia or
  hypotension
• Give animals access to water

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Loop Diuretic-FurosemideLASIX

• Most commonly used diuretic in veterinary
  medicine.
• Inhibits Na reabsorption in the LOH. Na stays in
  urine and so does water. DCT exchanges the Na for
  K, water stays in urine and potassium ions are
  lost in it.
• Diet may need to be supplemented with potassium.

Thiazide Diuretics- Chlorothiazide,Hydrochlorothia
zide

• Decrease reabsorption of sodium and chloride at
  the initial segment of the DCT.
• Like loop diuretics, sodium is exchanged for
  potassium and hypokalemia may develop.
• Does not diurese as much water as furosemide.

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Potassium-Sparing Diuretic- Spironolactone

• Cause sodium excretion and potassium
  conservation.
• Competitive antagonists of Aldosterone, so it
  reduces the amount of sodium reabsorbed. Sodium
  remains in the tubules and water follows it.

Osmotic Diuretic- Mannitol

• Not used for Cardiac-related diuresis, mainly for
  reducing cerebral edema and for flushing toxins.
• The molecules of Mannitol are excreted into the
  urine where they cause additional water to be
  excreted in the urine via osmosis.