Cardiac Drugs Flashcards
What is the mechanism of action of Digoxin?
Inhibits sodium-potassium ATP pump in cardiac muscle cells, results in increased intracellular calcium
What are some of the cardiac effects of Digoxin?
Increased inotropy Decreased left ventricular preload, afterload, wall tension, and oxygen consumption Increased stroke volume Decreased heart size Increases automaticity Decreases AV conduction
What happens to the Frank-Starling curve in a patient taking Digoxin?
Shifts to the left
How is Digoxin eliminated?
Primarily by kidneys with 35% excreted daily
Where is a tissue reservoir site for Digoxin?
Skeletal muscles - elderly have increased likelihood of elevated plasma levels due to decreased muscle mass
What is the MOA of Theophyline?
Nonselective PDE inhibitor that inhibits all fractions of PDE isoenzymes
How is Theophyline metabolized and excreted?
Metabolized by liver and excreted by kidneys
What is the MOA of milrinone?
Inhibition of PDEIII (phosphodiesterase enzyme III) that leads to increased intracellular concentrations of cAMP and cGMP that ultimately cause inward movement of calcium ions
What are the primary effects of milrinone?
Positive inotropy with vascular and airway smooth muscle relaxation
What are some clinical signs of digitalis toxicity?
Anorexia Nausea Vomiting Transitory amblyopia and scotomata Pain simulating trigeminal neuralgia Extremity pain
What is the normal plasma concentration for Digoxin?
0.5-2.5 ng/mL, >3 ng/mL indicates toxicity
How does hyperkalemia affect Digoxin?
reduces enzyme-inhibiting actions of glycosides and reduces the effects of Digoxin
What is the mechanism of action of class 1 antirhythmics?
sodium channel blockers, prolongs phase 0
What is the mechanism of action of class 2 antirhythmics?
beta blockers, decreases phase 4 slope
What is the mechanism of action of class 3 antirhythmics?
potassium channel blockers, elongates phase 3 and increases effective refractory period
What is the mechanism of action of class 4 antirhythmics?
calcium channel blockers, prolongs phase 0
What class of antirhythmic is Procainamide?
Class 1A
What is the mechanism of action of Procainamide?
blocks sodium channels and prolongs upstroke of the action potential, slows conduction, and prolongs the WRS duration on ECG
also prolongs APD by nonspecific blockade of potassium channels
What property of Procainamide causes hypotension?
Ganglion-blocking properties that reduces peripheral vascular resistance
What are Procainamide’s toxic effects?
excessive action potential prolongation, QT-interval prolongation, and induction of Torsades and syncope
What are some side effects of Procainamide?
Lupus-like symptoms Hypotension Nausea Diarrhea Rash Rarely - pleuritis, pericarditis, agranulocytosis, hepatitis
How is Procainamide metabolized?
metabolite metabolized hepatically
What is a metabolite of Procainamide and what is its significance?
NAPA, can cause Torsades if accumulated
How is Procainamide eliminated and what is its half-life?
Kidneys, half life of 3-4 hours
What are the clinical indications of using peripheral vasodilators
treat hypertensive crises, produce controlled hypotension, and facilitate LV forward stroke volume
Does SNP dilate veins, arteries, or both?
Both; decreases preload and after load
What is a molecule of SNP made of?
1 nitro group and 5 cyanide molecules
How is SNP metabolized
hemoglobin
How are the cyanide molecules generally eliminated?
Rodinase enzyme causes the cyanide to be attached to Vit B12 ( thiocyanate) which is then excreted by the kidneys
What is the onset of SNP?
immediate
What is the DOA of SNP?
3-5 minutes
What is the standard dose of SNP?
0.3-10mcg/kg/min
What could be a detrimental effect of SNP?
reflex tachycardia, leading to increased O2 demand and potentially cause myocardial ischemia
SNP molecule is what percent cyanide?
44%
What is the purpose of controlled hypotension
operations that require a bloodless field and reduced blood loss
Why is SNP good to use for hypertensive emergencies?
ease of titration, rapid onset, short DOA, and efficacy
Which drug has a risk of causing cyanide toxicity
SNP
What are the effects of cyanide toxicity?
tissue hypoxia, anaerobic metabolism, and eventually death
What is the treatment for cyanide toxicity?
3% sodium nitrate, sodium thiosulfate, Vit B12, discontinue infusion, treat acidosis, administer 100% O2
Does hydralazine dilate veins, arteries, or both?
arteries; decreases after load
What is the standard dose of hydralazine?
2.5-10mg IV
What is the onset of hydralazine?
10-20 minutes
Metabolism/excretion of hydralazine?
liver/renal
Does hydralazine decrease SBP or DBP more?
DPB
What is the DOA of hydralazine?
unpredictable
Does nitroglycerin dilate veins, arteries, or both?
veins primarily; decreases preload; can cause arterial dilation at higher doses
Which vasodilator is most commonly used for angina
nitroglycerin
What is the MOA of nitroglycerin?
contains a nitro group which contributes to NO mediated vasodilation
What is the onset of nitroglycerin?
2-5 minutes
What is the DOA of nitroglycerin?
5-10 minutes
Which drug to people develop rapid tolerance to?
nitroglycerin
What can be done to reverse nitroglycerin tolerance?
a drug free interval of 12-14 hours
T/F: Nitroglycerin reduces myocardial ischemia primarily by dilating coronary arteries and increasing blood supply to the myocardium?
F: reduces ischemia primarily by reducing preload and therefore reducing myocardial oxygen consumption
What are SE of nitroglycerin?
Headache, flushing, decreased sensitivity to heparin
Which vasodilator is effective in reducing sphincter of Oddi spasm?
nitroglycerin
Is tachycardia more marked with A1 or A2 antagonists?
A2 because they increase NE release increasing B1 stimulation at the heart
Phentolamine has what effect at A1 and A2 receptors
A1=A2 antagonist
What are some adverse effects related to Phentolamine administration
cardiac stimulation, tachycardia, arrhythmias, myocardial ischemia
What are clinical uses of phentolamine
pheochromocytoma excision, HTN crisis, extravascular administration of sympathomimetic agents
What is dose of phentolamine?
30-70mcg/kg IV
What effect does prazosin have on a1 vs. a2 receptors?
a1»»»a2 antagonist
Why is prazosin’s reduced a2 activity beneficial
results in relative absence of tachycardia
What are the clinical uses of Prazosin?
preop prep for patients with pheo, essential HTN, decreasing after load in patients with heart failure, raynaud phenomenon
What are some EKG changes associated with Digoxin?
Scooped ST
Biphasic T wave
Shortened QT
Long PR
How long does it take to see effects of Digoxin administered IV?
5-30 minutes
If a patient has kidney disease, should the Digoxin dose be decreased? And if so, by how much?
Eliminated via kidneys so dose needs to be decreased by 75%
Does Digoxin have any effects on someone with normal cardiac function?
No
How can Digoxin be used in anesthesia?
Can be administered prophylactically to someone with limited cardiac reserve or in patients with CAD recovering from anesthesia (administered day before surgery and 0.25 mg given before induction)
What are the dosing recommendations for Digoxin?
0.125 - 0.25 mg/day
What can speed the metabolism of Theophylline?
Cigarettes
What is the loading/maintenance dose of Theophylline?
Loading dose of 5 mg/kg IV followed by infusion of 0.5 - 1 mg/kg/hr
What are some of the cardiac effects of Calcium?
Intense positive inotropy (lasts 10-20 minutes)
Increased stroke volume
Decreased left ventricular end-diastolic pressure
Decreased heart rate
Decreased systemic vascular resistance
When would it be ideal to administer Calcium during anesthesia?
At the end of cardiopulmonary bypass to improve contractility and stroke volume–patients usually hypocalcemic from cardioplegic solutions and citrated blood
Which contains more calcium: 10% calcium chloride or 10% calcium gluconate?
10% Calcium chloride (should only be administered via central line)
What are the dosing recommendations for calcium?
5 to 10 mg/kg IV (Stoelting)
What is the mechanism behind hypotension caused by Milrinone?
Inhibits PDEIII –> Increased cAMP –> EFFLUX of calcium from smooth muscle cells –> vasodilatation
(cAMP acts opposite in smooth muscle cells than cardiac muscle cells)