Unit 10 - Cardiovascular Drugs (1)

Compensatory Mechanisms of the Cardiovascular System

The cardiovascular system has a built-in reserve capacity which allows it to increase its output during times of need and to compensate for cardiac disease. The four basic compensatory mechanisms include:

Objectives in the Treatment of Cardiovascular Disease

Basic objectives in the treatment of cardiovascular disease include:

Autonomic Nervous System Review

The autonomic nervous system is a network of nerves throughout the body that control unconscious processes. The autonomic nervous system breaks down into three divisions, each with its own job:

Receptors in the Body for the Autonomic Nervous System

Cardiovascular Drugs

Drugs which affect the ANS will have a variety of effects in the body. We choose drugs which target the specific organ or body part we need to influence. 5 categories:

Anti-arrhythmic = Negative Inotropes

Negative inotrope slows the heart. Lidocaine is a sodium channel blocker used for control of pre-ventricular contractions (PVC).

β1 blockers = β1 antagonists

Block β1 receptors to block the SNS. Drugs in this group end in "olol". Examples:Propanolol, Carvedilol, Atenolol.

Diltiazem

Calcium channel blocker used for cats with hypertrophic cardiomyopathy.

Positive Inotropes

Increase strength of contraction of the heart by increasing availability of calcium. Examples:Epinephrine, Dopamine, Pimobendan.

Anticholinergic

Atropine works against acetylcholine and is used to treat bradycardia, reduce salivation and bronchial secretions.

Vasodilators

Counteract arterial vasoconstriction caused by the SNS

Anti-arrythmic=Negative Inotropes

Negative inotrope- slows the heart

*Caution with all negative inotropes- DO NOT use in CHF animals**

Lidocaine

Anti-arryhtmic drug

• Without epinephrine

• Sodium channel blockers so nerves can not depolarize quickly

• Used as IV bolus or infusion

• Used for control of pre-ventricular contractions (PVC)

Adverse side effects: Cats much more sensitive (Can cause 1/3 or complete A-V block), Toxic side effects in CNS, toxic dose (10mg/kg=sedation, larger overdose= seizures)

Procanimide and Quinidine

Anti-arrythmic drug

• Human drug

• Same family as lidocaine

• Orally

• Used for atrial fibrilation (A-fib), PVCs, and ventricular tachycardia

B1 blockers=B1 antagonists

anti-arrythmic drug

• Block B1 receptors so blocks the SNS

• Drugs end in “olol”

• Slow depolarization of heart

  • Slows HR

Ex:

Propanol (Human)

Carvedilol & Atenolol (Human)-Newer B1 blockers=more specific to heart (less bronchoconstriction)

Adverse side effects: Up regulation of B receptors on heart-Increases number of B receptors so will need more drug over time as there are more receptors to block. If withdraw B blocker quickly, heart becomes sensitive to epinephrine

Dilitazem

Anti-arrythmic drug

• Calcium channel blocker

• Human drug

• Used for cats with hypertrophic cardiomyopathy

*Caution with all negative inotropes- DO NOT use in CHF animals

Positive Inotropes

Increase strength of contraction of heart by increasing availability of calcium.

Epinephrine

Positive Inotropes Drug

• Stimulates most a and B receptors

• Used for cardiac standstill

• Very short half life

Dopamine

Positive Inotropes drug

• Human drug

• More selective than epi

• Stimulates myocardial contractions

• some CNS stimulation

Adverse side effects: short half life, Downregulation, Heart decreases number of B receptors and is less responsive over time

Pimobendan

Positive Inotropes Drug

• Acts as both a vasodilator and a positive inotrope

• Treats CHF due to dilated cardiomyopathy (DCM) in dogs

  • Vetmedin

Anticholinergic- Atropine

Works against acetylcholine

• Parasympatholytic

• Used to treat bradycardia, reduce salivation and bronchial secretions before surgery or as an antidote for overdose of cholinergic

Vasodilators

Counteract arterial vasoconstriction caused by the SNS

• Responding to decreased BP due to congestive heart Failure

Reverse vasoconstriction

• Start of slowly or can cause hypotension

• Seen as lethargy, ataxia, syncope

Amlodipine

Arterial Vasodilator

• antihypersensitive/Antianginal

Classified as a calcium channel blocker

• Relaxation of smooth muscle lining the arterioles

Used to treat secondary hypertension in cats

Hydralazine

Arterial Vasodilator

Causes arteriolar smooth muscle to relax

Used to treat Congestive Heart Failure (CHF)

Nitroglycerin

Venous Vasodilator

Human drug

Used to treat pulmonary edema from CHF and improve cardiac output

Dilates coronary arterioles to improve blood flow

Significant first pass effect=not given PO

• applied topically- use gloves!

Mixed Vasodilators

Used to treat CHF

Drugs often end in “pril”

• Enalapril

• Benzaprol (Fortekor)

  Adverse side effects: decrease potassium excretion in the kidneys so can see hyperkalemia

Diuretics

Remove excess fluid by increasing water loss in urine

Used to treat pulmonary edema from CHF or cerebral edema

All diuretics:

1. Preventing reabsorption of either Na or K from renal tubules

2. Increasing secretion of either Na or K from renal tubules

Na or K takes water with it by osmosis

Furosemide

Diuretic

Loop diuretic (loop of henle)

Prevents reabsorption of Na from urine

• Salix

• Lasix

Since Na is important, the DCT then reabsorbs the Na in exchange for K.

Adverse side effects: Cause K+ loss which effects heart function, Ototoxicity

Trichlormethiazide

Diuretic

Inhibit reabsorption of Na and Cl

• Naquasone- also has dexmethasone for inflammation

  • injection for cattle and horses

Adverse side effects: Na will be reabsorbed in exchange for K so can also get hypokalemia

Mannitol

Diuretic

Carbohydrate (sugar)

Osmotic diuretic

Used for cerebral edema

alleviates pressure in eyes

Acetylsalicylic Acid = Aspirin

interferes with platelet clumping

• Spontaneous formation of platelet plugs (thrombi) occurs in cardiomyopathies

• Aspirin will prevent formation of thrombi which prevents stroke or myocardial infarcts

Urinary Incontinence

Sympathomimetic Agents = a adrenergic

• Phenylpropanolamine

  • Propalin

• Stimulates the urethral sphincter muscle

• Spayed female dogs

• Do not use with CV drugs such as B blockers or atropine

Adverse side effects: Behavioural-(aggression, restless), Cardiovascular-tachycardia, V/D, seizures