Diuretics Facts Flashcards
three major applications of diuretics
treatment of hypertension
mobilization of edamatous fluid associated with heart failure, cirrhosis, or kidney disease
prevent renal failure
three main functions of the kidney
maintain ECF volume and composition
maintain acid-base balance
excrete waste products and toxic substances
diuretics work primarily with interfering with
reabsorption
_____% of filtered sodium and chloride are reabsorbed in the proximal convoluted tubule
65%
how much bicarbonate and potassium in filtrate is reabsorbed in the proximal convoluted tubule
essentially all
solutes and water are reabsorbed to an equal extent, making the tubular urine ______
remain isotonic
urine becomes concentrated in the
descending Henle loop (from 300 to 1200 mOsm/L
in the ascending loop of Henle, _____% of filtered sodium and chloride is reabsorbed
20%
the tonicity of the urine returns back to that of the original filtrate in the
ascending Henle loop (300mOsm/L) (not permeable to water)
in the distal convoluted tubule _____% of filtered sodium and chloride is reabsorbed
10%
mechanism of action of most diuretics
blockade sodium and chloride reabsorption
how diuretics work
by blocking reabsorption of Na and Cl, it creates osmotic pressure within the nephron that prevents the passive reabsorption of water. since they remain in the nephron, it promotes excretion of both
common side effects of diuretics
hypovolemia
electrolyte imbalance
acid-base imbalance
the most effective diuretics available are
loop diuretics (Henle loop)
the most common loop diuretic used is
furosemide (Lasix)
how does furosemide function
blocks sodium and chloride reabsorption in the ascending loop, passively preventing reabsorption of water. because of the large amount of Na and Cl blocked (20%) it can cause profound diuresis
pharmacology of loop diuretics
acts quickly (60 mins orally, 5 mins IV)
lasts 5 hrs PO, 2 hrs IV
conditions that justify loop diuretics are
pulmonary edema from CHF
edema that has been unresponsive to less efficacious diuretics
hypertension that can’t be controlled with other diuretics
especially useful because can promote diuresis even with low GFR and RBF
adverse reactions of loop diuretics
dehydration
hypotension
hypokalemia (dysrhythmias)
ototoxicity (hearing impairment)
drug interactions of loop diuretics
digoxin (for heart failure and dysrhythmias) (hypokalemia cause problems)
ototoxic drugs
potassium-sparing diuretics (counter hypokalemia)
NSAIDs (decrease effect of diuretics)
different loop diuretics
furosemide (Lasix)
ethacrynic acid (Edecrin)
bumetanide (Bumex)
mechanism of action of thiazide diuretics
block reabsorption of Na and Cl in early segment of distal convoluted tubule
only 10% filtered NaCl is normally reabsorbed here so urine flow these drugs cause is much lower than loop diuretics
ineffective when GFR is low
pharmacology of thiazide
diuresis begins 2 hours after orally taken
peak within 4-6 hours
may last 12 hours
thiazide mainly used for
HTN
edema from mild to moderate heart failure
edema from hepatic or renal disease
adverse effects of thiazide
same as loop diuretics except not ototoxic
dehydration
hypotension
hypokalemia (dysrhythmias)
types of thiazide drugs
8 types and all end in thiazide
most common hydrochlorothiazide
all by mouth
spironolactone (Aldactone) (aldosterone antagonist) mechanism of action
blocks action of aldosterone in distal tubule
aldosterone increase sodium absorption and increase potassium excretion so it does the opposite
minimal diuresis
action delayed (up to 48 hours)
uses of spironolactone
HTN and edema
often used with loops or thiazides to prevent hypokalemia
block effects of aldosterone in patients with hyperaldosteronism
adverse effects of spironolactone
hyperkalemia
endocrine effects
*menstrual irregularity
*impotence
*deepening of voice
*gynecomastia
drug interactions - spironolactone
use with caution with drugs that elevate potassium and block aldosterone (ACEI, angiotensin receptor inhibitors, renin inhibitors, K+ sparing diuretics)
osmotic diuretics used
mannitol (Osmitrol)
there are others used, but only mannitol used for diuretic action
mechanism of action of osmotic diuretics
very different from other diuretics
*simple sugar that creates osmotic force in glomerulus
*freely filtered at the glomerulus
*little reabsorption
*not metabolized
*pharmacologically inert (no direct effects on biochemistry or physiology of cells)
*increases osmotic pressure of filtrate, water not reabsorbed and therefore excreted
*amount of diuresis directly related to amount of drug present
*little effect on secretion of electrolytes
*effective in reducing intracranial edema and therefore intracranial pressure (ICP)
pharmacology of osmotic diuretics
does not cross GI endothelium
given only IV - diuresis begins after 30-60 min and lasts 6-8 hours
uses of osmotic diuretics
prevent renal failure - drawing water into the nephron
reduce intracranial pressure (ICP) - presence in brain blood vessels creates osmotic force which pulls fluid from brain into blood
reduce intraocular pressure - creates osmotic force that pulls fluid into the blood
adverse reactions of osmotic diuretic
edema - when it exits capillaries, it draws water along