CHF Pharmacology

Question 1

what are the three main categories of drugs to treat congestive heart failure

Answer 1

1. diuretics
2. vasodilators
3. positive inotropes

Question 2

what drug classes reduce preload

Answer 2

diuretics
venodilators

Question 3

what drug class reduces afterload and MVO2

Answer 3

arteriodilators

Question 4

what are the common drugs used to treat heart failure in dogs

Answer 4

furosemide (lasix)
pimobendan
ACE inhibitors
spironolactone

Question 5

what are the common drugs used to treat heart failure in cats

Answer 5

furosemide
clopidogrel
ACE inhibitors

Question 6

what drug class should ALL CHF treatment include

Answer 6

diuretics

preferably loop diuretics

can be used in emergency and at home

Question 7

general mechanism of diuretics

Answer 7

prevents the reabsorption of Na, Cl, and H2O

increases water excretion to decrease plasma volume (decreases venous pressure, preload)

Question 8

mechanism of action of loop diuretics

Answer 8

inhibits Na/K/2Cl exchanger in thick ascending loop of henle

Question 9

loop diuretics examples

Answer 9

1. furosemide (lasix)
2. torsemide

Question 10

what is required in order to treat with furosemide

Answer 10

healthy kidney - must be actively secreted into tubule lumen

Question 11

use of furosemide vs torsemide

Answer 11

furosemide - rapid onset, short duration of action

torsemide - slower onset, long duration of action (chronic management of advanced CHF)

Question 12

mechanism of action of thiazide diuretics

Answer 12

inhibits Na/Cl co-transporter in the DCT

Question 13

example of thiazide diuretic

Answer 13

hydrochlorothiazide (HCTZ)

Question 14

use of HCTZ

Answer 14

used in conjunction with loop diuretic (furosemide) to increase the potency by extending Na/water excretion to the DCT

can cause additional ion loss but increases Ca retention

Question 15

mechanism of action of potassium sparing diuretics

Answer 15

blocks the action of aldosterone in the collecting ducts

Question 16

example of a potassium sparing diuretic

Answer 16

spironolactone

Question 17

use of spironolactone

Answer 17

blocks the activity of Na/K ATPase to reduce Na reabsorption and K excretion

weak diuretic - used in conjunction with furosemide

Question 18

what do venodilators decrease

Answer 18

preload

Question 19

what do arteriodilators decrease

Answer 19

afterload (by decreasing regurgitant fraction)

Question 20

regurgitant fraction

Answer 20

percentage of blood in the LV that regurgitates back into the LA

Question 21

categories of vasodilators

Answer 21

1. direct acting
2. Ca channel blockers
3. RAAS inhibitors
4. sympatholytic agents
5. phosphodiesterase inhibitors

Question 22

mechanism and example of direct acting vasodilators

Answer 22

relax smooth muscle without blocking constrictor mechanisms

sodium nitroprusside

Question 23

mechanism and example of Ca channel blockers

Answer 23

decrease Ca influx into smooth muscle

amlodipine, clevidipine

Question 24

mechanism and example of RAAS inhibitors

Answer 24

block production or effect of ANG II

ACE inhibitors, ANGII receptor blockers (ARBs)

Question 25

mechanism of sympatholytic agents

Answer 25

block alpha receptors

Question 26

mechanism and example of phosphodiesterase inhibitors

Answer 26

increase cAMP to cause smooth muscle relaxation; also causes cardiac muscle contraction pimobendan

Question 27

why is blocking the RAAS cascade used to treat CHF

Answer 27

RAAS gets overstimulated in CHF ANG II + aldosterone cause excess vasoconstriction and Na/H2O reabsorption, leading to cardiac hypertrophy/fibrosis/remodeling decreasing RAAS will reduce the adverse effects

Question 28

mechanism of ACE inhibitors

Answer 28

block the conversion of ANG I to ANG II requires activation by hepatic metabolism

Question 29

ACE inhibitor examples

Answer 29

enalapril, benazepril

Question 30

side effect of ACE inhibitors

Answer 30

dilates afferent arteriole resulting in decreased glomerular pressure causes GFR to decrease and creat/BUN to accumulate leading to acute azotemia kidney will accommodate if animal does well through initial azotemia

Question 31

amlodipine vs clevidipine uses

Answer 31

amlodipine: treats systemic hypertension by reducing afterload; can be used even if patient with MV disease is not hypertensive clevidipine: IV administration; used in ER as a CRI

Question 32

sodium nitroprusside uses

Answer 32

ER treatment of life threatening pulmonary edema or systemic hypertension in dogs by decreasing LV afterload (reduces MVO2 and regurgitation) myxomatous MV disease more common use than DCM

Question 33

mechanism of action of positive inotropes

Answer 33

increases intracellular Ca availability OR sensitivity to Ca

Question 34

examples of positive inotropes

Answer 34

pimobendan digoxin dobutamine

Question 35

pimobendan mechanism

Answer 35

PDE inhibitor; prevents degradation of cAMP to increase signaling in cardiac cells AND sensitizes the contractile apparatus to Ca ALSO works in vascular smooth muscle to increase cAMP leading to dilation

Question 36

why is pimobendan considered an "inodilator"

Answer 36

increases inotropy in the heart AND relaxes vascular smooth muscle (dilation)

Question 37

why does pimobendan have a lower risk of Ca induced arrhythmias than other positive inotropes

Answer 37

because it does not increase intracellular Ca increases cAMP signaling and increases sensitivity to Ca

Question 38

digoxin mechanism

Answer 38

inhibits Na/K ATPase to activate Na/Ca exchanger and increase Ca influx resulting in positive inotropy

Question 39

how does digoxin affect baroreceptors

Answer 39

increases vagal tone and decreases sympathetic input

Question 40

what is the main use of digoxin

Answer 40

decrease heart rate during atrial fibrillation can be used for concurrent CHF and atrial fibrillation

Question 41

mechanism of dobutamine

Answer 41

catecholamine; stimulates B1 receptors and increases cAMP to increase Ca influx B1 selective but also has minor B2 and a1/2 effects allows for positive inotropy with minimal vasoconstriction (no net effect on BP)

Question 42

use of dobutamine

Answer 42

used in ER for treatment of cardiogenic shock less used than pimobendan because it increases workload on the heart

Question 43

what species requires anti platelet therapy included in treatment of CHF

Answer 43

cats - highly predisposed to thrombosis during heart failure (Virchow's triangle)

Question 44

what anti platelet therapy is most commonly used

Answer 44

clopidogrel

Question 45

clopidogrel mechanism

Answer 45

decreases platelet stickiness