Cardiovascular Pharmacology Flashcards
In what 3 ways does the cardiovascular system increase or decrease cardiac output?
- changes heart rate
- adjusts myocardial contractility
- optimizes vascular size
What are the 3 physiological controls of cardiac function?
- pressure sensors
- sympathetic and parasympathetic nervous systems
- renin-angiotensin-aldosterone system (RAAS)
drugs most often exert their effect by stimulating or blunting these systems
How is the ANS able to regulate the cardiovascular system?
adjusts heart rate (β1 receptors), vascular volume (α1 and α2 receptors), and myocardial contractility
What determines intrinsic heart rate?
sympathetic and parasympathetic nervous systems
- AT REST = PSNS is dominant, resulting in a resting heart rate lower than the intrinsic heart rate
- HEART FAILURE = SNS is dominant, resulting in high resting heart rate
What does sympathetic stimulation of cardiac muscle result in? Parasympathetic stimulation?
increased force of contraction independent of muscle length (inotropy), which enhances cardiac output over the basal state
slows heart rate and increases ventricular filling time
What are the 3 functional classification schemes of cardiac disease in dogs?
- New York Heart Association (NYHA) - I, II, III, IV
- International Small Cardiac Health Council (ISACHC) - Ia, Ib, II, IIIa, IIIb
- American College of Veterinary Internal Medicine (ACVIM): A, B1, B2, C1, C2, D1, D2
What digitalis glycoside is used as a positive inotrope? What 4 effects does it have on patients with failing hearts? What does it not affect?
digoxin derived from the purple foxglove plant (Digitalis purpurea)
- increases myocardial contractility (inotropism)
- increases cardiac output
- increases diuresis with reduction of edema secondary to decreased sympathetic tone
- reduction in heart rate
myocardial oxygen consumption
What is the mechanism of action of digoxin? What does this cause?
inhibits the Na/K ATPase (sodium pymp) in cardiac myocytes causing an increase in intracellular Na, which augments a transmembrane exchange of Na for extracellular Ca
increased Ca stored in sarcoplasmic reticulum increases the amount of Ca released by each action potential —> inotropism
How does digoxin affect cardiac output? Vagal tone? Sympathetic activity? Parasympathetic activity?
increases contractility of both normal and failing* myocardium, but has minor effect on output
indirectly increases vagal tone by a cholinergic parasympathomimetic effect
decreases
stimulates parasympathetic activity, resulting in a negative chronotropic effect (decreased heart rate, force is more important than consistency)
What form of digoxin is best absorbed following oral administration? What follows biotransformation? How is it eliminated?
elixir > tablet
enterohepatic circulation
urinary
What are the 3 main indications for digoxin?
- CHF
- supraventricular tachyarrhythmias
- dilated cardiomyopathy (DCM)
What are the 5 most common clinical signs associated with digoxin?
- mild gastrointestinal upset
- inappetence
- depression
- loose stool
- vomiting
often self-limiting
What are the 2 most common sympathomimetic agents used as positive inotropes?
- Dobutamine
- Dopamine
What is the mechanism of action of Dobutamine in the cardiovascular system? What additional effect does it have?
improved cardiac performance by binding β1 myocardial receptors and uses secondary messengers to increase intercellular calcium
weak action on α-receptors
How must Dobutamine be administered? What is its major indication?
IV constant rate infusion due to its very short half-life (not meant for long term therapy)
short term inotropic in dogs and cats with acute myocardial failure emergency
What is the mechanism of action of Dopamine on the cardiovascular system? How must it be administered?
intermediate dosages has positive effects on cardiac contractility, heart rate, and cardiac output (low dose = vasodilation by stimulating D1 and D2 receptors; high dose = α and β receptors)
IV constant rate infusion
What are iodilators? Which one is most commonly used in vet med?
vasodilatory and positive inotropic properties
Pimobendan (Vetmedin)
What are the 2 mechanisms of action of Pimobendan (Vetmedin)? What is its indication?
- increases myocardial contractility by increasing calcium affinity
- inhibits phosphodiesterase III in blood vessels, that metabolize cAMP and is responsible for vasodilation
clinical management of canine heart failure caused by DCM
Why isn’t Pimobendan (Vetmedin) not commonly used in heart failure in cats?
heart failure in cats is most likely caused by hypertrophic cardiomyopathy, so increased force of contraction is not helpful
How is Pimobendan metabolized? How is it excreted?
metabolized into an acitve metabolite (O-desmethyl-pimobendan), a potent inhibitor of phosphodiesterase III
bile —> feces
Pimobendan is well tolerated in dogs. What is the most common adverse effect?
GI effects - reduced appetite, diarrhea
When is the use of Pimobendan and other positive inotropes contraindicated?
patients with outflow tract obstruction
What additional effect does Pimobendan have?
blocks the formation of the cytokines, TNF-α, IL-1β, and IL-6, that are typically elevated in patients with heart failure and depress myocardial contractility
Why would rectal administration of Pimobendan (Vetmedin) be beneficial?
- rectal absorption is similar to oral when higher (2x) doses are administered
- oral administration is difficult in emergency situations
- different parts of the rectum undergo 1st pass metabolism
How does the renin-angiotensin-aldosterone system work? What aspects of heart failure induce this system?
- angiotensinogen is metabolized into angiotensin I by renin released from the kidneys
- ACE converts angiotensin I into angiotensin II
- angiotensin II in the serum induces a thirst response, vasoconstriction, and aldosterone synthesis
decreased BP, renal blood perfusion, and NaCl and increased SNS innervation induced the release of renin from the kidney —> chronicity = toxic
How are ACE inhibitors used to treat heart failure?
- blockage of angiotensin II and aldosterone production blunts the negative effects of pathological remodeling of the heart, vasculature, and kidney in states of pathological RAAS activation
- also inhibit bradykinin inactivation, blocking RAAS-induced vasoconstriction
What are the most common prodrugs used as ACE inhibitors? Which parent drug is used? Why are prodrugs preferred?
- Captopril (Capoten)
- Enalapril (Enacard, Vasotec) —> enalaprilat
- Benazepril (Fortekor) —> benazeprilat
- Ramipril (Altace, Vasotop) —> ramiprilat
- Imidapril (Prilium) —> imidaprilat
Lisinopril (Prinivil, Zestril)
prodrugs have improved bioavailability (parent drug tends to have decreased absorption)
What are the 4 major indications of ACE inhibitors? What levels of heart disease is this considered?
- systolic heart failure
- subclinical myxomatous mitral valvular disease
- systemic hypertension
- proteinuric renal disease
NYHA: I
ISACHC: Ia, Ib
ACVIM: B1, B2
What ACE inhibitor is preferentially used for NYHA phase III and IV heart disease caused by MMVD in dogs?
Enalapril
- less GI adverse effects
- decreased pulmonary edema
What ACE inhibitor is not commonly used anymore?
Captopril —> GI upset common
In what 3 ways does ACE inhibitors help in chronic kidney disease?
- reduces intraglomerular pressure
- decreases proteinuria
- slows down progression of lesions
Can ACE inhibitors be used with other cardiovascular drugs? What are 2 types of drugs they commonly interact with?
YES - very safe
- diuretics - potentiates effects, use reduced doses
- NSAIDs - decreases beneficial effect of ACE inhibitors by blocking the formation of prostaglandins that have antihypertensive action
How does the excretion of Enalapril/Enalaprilat and Benazepril/Benazeprilat? Which ACE inhibitor is affected by the presence of food in the GIT?
- E = urinary
- B = equally in urinary and bile in dogs; mostly feces and some urinary in cats
Captopril —> decreased bioavailability
What are 3 common adverse effects of ACE inhibitors?
- hypotension - especially when used in conjunction with vasodilators, diuretics, and sodium restriction
- azotemia, inappetence, weakness, lassitude
- reduction in kidney perfusion pressure and GFR, which worsens azotemia
How can azotemia and other adverse effects of ACE inhibitors be reversed?
diuretic cessation or reduction in dosage
What are some less common adverse effects of ACE inhibitors seen in humans?
coughing and angioedema
- no related to increased bradykinin
