CHF Pharmacology Flashcards
what are the three main categories of drugs to treat congestive heart failure
- diuretics
- vasodilators
- positive inotropes
what drug classes reduce preload
diuretics
venodilators
what drug class reduces afterload and MVO2
arteriodilators
what are the common drugs used to treat heart failure in dogs
furosemide (lasix)
pimobendan
ACE inhibitors
spironolactone
what are the common drugs used to treat heart failure in cats
furosemide
clopidogrel
ACE inhibitors
what drug class should ALL CHF treatment include
diuretics
preferably loop diuretics
can be used in emergency and at home
general mechanism of diuretics
prevents the reabsorption of Na, Cl, and H2O
increases water excretion to decrease plasma volume (decreases venous pressure, preload)
mechanism of action of loop diuretics
inhibits Na/K/2Cl exchanger in thick ascending loop of henle
loop diuretics examples
- furosemide (lasix)
- torsemide
what is required in order to treat with furosemide
healthy kidney - must be actively secreted into tubule lumen
use of furosemide vs torsemide
furosemide - rapid onset, short duration of action
torsemide - slower onset, long duration of action (chronic management of advanced CHF)
mechanism of action of thiazide diuretics
inhibits Na/Cl co-transporter in the DCT
example of thiazide diuretic
hydrochlorothiazide (HCTZ)
use of HCTZ
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
mechanism of action of potassium sparing diuretics
blocks the action of aldosterone in the collecting ducts
example of a potassium sparing diuretic
spironolactone
use of spironolactone
blocks the activity of Na/K ATPase to reduce Na reabsorption and K excretion
weak diuretic - used in conjunction with furosemide
what do venodilators decrease
preload
what do arteriodilators decrease
afterload (by decreasing regurgitant fraction)
regurgitant fraction
percentage of blood in the LV that regurgitates back into the LA
categories of vasodilators
- direct acting
- Ca channel blockers
- RAAS inhibitors
- sympatholytic agents
- phosphodiesterase inhibitors
mechanism and example of direct acting vasodilators
relax smooth muscle without blocking constrictor mechanisms
sodium nitroprusside
mechanism and example of Ca channel blockers
decrease Ca influx into smooth muscle
amlodipine, clevidipine
mechanism and example of RAAS inhibitors
block production or effect of ANG II
ACE inhibitors, ANGII receptor blockers (ARBs)
mechanism of sympatholytic agents
block alpha receptors
mechanism and example of phosphodiesterase inhibitors
increase cAMP to cause smooth muscle relaxation; also causes cardiac muscle contraction
pimobendan
why is blocking the RAAS cascade used to treat CHF
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
mechanism of ACE inhibitors
block the conversion of ANG I to ANG II
requires activation by hepatic metabolism
ACE inhibitor examples
enalapril, benazepril
side effect of ACE inhibitors
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
amlodipine vs clevidipine uses
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
sodium nitroprusside uses
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
mechanism of action of positive inotropes
increases intracellular Ca availability OR sensitivity to Ca
examples of positive inotropes
pimobendan
digoxin
dobutamine
pimobendan mechanism
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
why is pimobendan considered an “inodilator”
increases inotropy in the heart AND relaxes vascular smooth muscle (dilation)
why does pimobendan have a lower risk of Ca induced arrhythmias than other positive inotropes
because it does not increase intracellular Ca
increases cAMP signaling and increases sensitivity to Ca
digoxin mechanism
inhibits Na/K ATPase to activate Na/Ca exchanger and increase Ca influx resulting in positive inotropy
how does digoxin affect baroreceptors
increases vagal tone and decreases sympathetic input
what is the main use of digoxin
decrease heart rate during atrial fibrillation
can be used for concurrent CHF and atrial fibrillation
mechanism of dobutamine
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)
use of dobutamine
used in ER for treatment of cardiogenic shock
less used than pimobendan because it increases workload on the heart
what species requires anti platelet therapy included in treatment of CHF
cats - highly predisposed to thrombosis during heart failure (Virchow’s triangle)
what anti platelet therapy is most commonly used
clopidogrel
clopidogrel mechanism
decreases platelet stickiness
