Chapter 40 Vasodilators Flashcards
What effects do vasodilator drugs have
they act directly on the smooth muscles in arterioles and veins to produce vessel relaxation
What do hydralazine and minoxidil cause dilation of?
selective dilation of arterioles
What does Nitroprusside cause dilation of?
arterioles and veins
If a drug dilates arterioles what are the effects?
decrease in cardiac afterload (the force the heart works against to pump blood).
If drugs dilate capacitance vessels (veins) what are the effects
reduce the force with which blood is returned to the heart, which reduce ventricular filling. This reduction in filling decreases cardiac preload (the degree of stretch of the ventricular muscle before contraction), which decreases the force of ventricular contraction.
Vasodilators therapeutic uses
essential htn, htn crisis, angina pectoris, heart failure, and MI
AE of vasodilation
postural hypotension-
caused by venous relaxation, gravity causes blood to pool in the veins, thereby decreasing venous return to the heart, which causes decreased cardiac output, and decrease in blood pressure
minimal in recumbent subjects because the effect of gravity on venous return is small when we are lying down.
Hydralazine Cardiovascular Effects
selective dilation of arterioles (little no effects on veins)
dilation results from direct action on VSM (vascular smooth muscle)
peripheral resistance and arterial blood pressure fall, while HR and myocardial contractility increase d/t reflex mechanism -> means decreased cardiac output
postural hypotension is minimal bc it works selectively on arterioles
Hydralazine Kinetics
PO: effects begin within 45 minutes and persist for six hours or longer
Parenteral admin: effects begin faster (within 10 minutes) and last 2 to 4 hours.
Hydralazine Metabolism
inactivated by a metabolic process known as acetylation - either genetically slower or faster. -
if slow - higher drug in serum
if fast - lower
genetically determined
What would occur in a person who metabolized hydral slowly due to acetylate?
excessive vasodilation with undersired effects
reduce drug in slow acetylators
Therapeutic uses of hydralazine
lower blood pressure in patients with essential hypertension
regimen almost always included a B blocker, used largely in the past but now replaced by newer antihypertensive agents.
Heart failure- reduce afterload in pt with hf, tolerence develops (usually used with isosorbide dinitrate)
AE of hydralazine
trigger reflex stimulation of the heart, thereby causing cardiac work and myocardial oxygen demand to increase
bc hydralazine induced REFLEX TACHYCARDIA is frequently severe, usually combined with a b blocker
Systemic Lupus erythematosus-like syndrome (symptoms include muscle pain, joint pain, fever, nephritis, pericarditis - SMA SYPTOMS -discontinue drug in this case
most likely in slow metabolizers, d/c hydral if it occurs
usually reversible - may take a long time for SMA symptoms to resolve
Hydral drug interactions
combined with a B blocker to protect agaisnt reflex tachycardia and a combined with a diuretic to prevent na and water retention and expansion of blood volume
if used with other hypotensive medications care is needed to prevent excessive hypotension
in HF combined with isosorbide dinitrate (dilates veins)
What patient would you use minoxidil for?
severe hypertension unresponsive to other drugs
d/t intense vasodilation with more severe adverse reactions
Minoxidil cardiovascular effects
selective dilation of arterioles little or no venous dilation occurs
-arteriolar dilation decreases perpheral resistance and arterial pressure
-so
increase HR and myocardial contractility
Which increase cardiac oxygen demand and can make angina worse
What must minoxidle be metabolized to in order to make the drug effective?
minxidil sulfate which causes k channels to open which hyperpolarizes VSM cells, which reduces their ability to contract
Minoxidil Kinetics
maximum vaso within 2-3 hrs then gradually declines.effects may continue 2-3 days.
metabolites and parent drug are eliminated in the urine
half life 4.2 hours
Minoxidil therapeutic uses
severe hypertension reserved only for pts who have not responded to safer drugs
What drug do you combine with minoxidil to minimize adverse effects?
b blockers and intensive diuretic therapy (loop diuretic alone or in combo with a thiazide diuretic)
if that doesn’t work - dialysis, then or d/c drug
AE of minoxidil
reflex tachycardia- combine with b blocker
na and water retention- volume expansion may be so severe as to cause cardiac decompensation. Must give with diuretics (loop and/ or thiazide) if not effective pt must be put on dialysis or minoxidil withdrawn
hypertrichosis- excessive hair growth (Rogaine)
What is the black box warning for minoxidil?
can cause pericardial effusion, occasionally progressing to tamponade, and may exacerbate angina pectoris
What should be monitored on a daily bases for patient taking vasodilators?
blood pressure and heart rate
for minoxidil- also include daily weights
Vasodilators and pregnant
Avoid if possible
