2B : DIURETICS - OSMOTIC DIURETICS Flashcards
OSMOTIC DIURETICS
DRUGS
glycerin, isosorbide, mannitol , urea
Prototype :
Mannitol
SITE OF ACTION
LoH & PT
MOA
decreases H2O reabsorption by
increasing osmotic pressure of tubular fluid
Osmolality retains
water in tubule
Effects of MANNITOL
- increased urine volume
- increased urinary excretion of most solutes & nearly all electrolytes
- greatly increased Na+ excretion (accelerated rate of urine flow through tubule; Na+ transporters cannot handle volume rapidly
enough) - reduces brain volume & ICP
by osmotically extracting H2O from tissues into the blood
(similar effect in eye)
Therapeutic uses of
Osmotic Diuretics
- Increasing urine volume in oliguric ATN
- Dialysis Disequilibrium Syndrome
- Extraction of H2O from the brain
- Reduction of Intraocular Pressure
Mannitol
may provide renal protection by :
- removing obstructing tubular casts
- diluting nephrotoxic substances
- reducing swelling of tubular elements via osmotic extraction of H2O
true or false
Pts who respond will recover more rapidly & require less dialysis
true
mannitol
& urea role in dialysis disequilibrium syndrome
increase ECF osmolality ,
causes water to shift back to ECF
Pharmacokinetics of mannitol
poorly absorbed from the GI tract when administered orally causing an osmotic diarrhea
must
be given for _____ systemic
effects
parenterally
true or false
osmotic diuretics are excreted by glomerular filtration within 30-60 mins without any important reabsorption, secretion or metabolism
true
MANNITOL: Effects on
Renal Hemodynamics
- increases Renal Blood Flow
by various mechanisms - dilates afferent arteriole
how can mannito; increase RBF
- expands ECF volume
- decreases blood viscosity
- inhibits renin release
all effects of extracting water from intracellular compartments
Absorption and Elimination
Mannitol
- parenteral
- oral administration causes osmotic diarrhea
- T1/2 (h) 0.25 to 1.7 in renal failure
- min metabolism, excreted by
glomerular filtration within
30 60min, no important tubular reabsorption or secretion
Absorption and Elimination
Glycerin &
Isosorbide
orally active, elimination ~80%
metabolism
Toxicity & Adverse Effects
common AE :
- headache, nausea, vomiting
- hyponatremia from extraction of H2O
- hypernatremia & dehydration resulting from loss of H2O in excess of electrolytes
- hyperkalemia from increased intracellular K+ concentration
- frank pulmonary edema
in pts with HF or pulmonary
congestion - resulting from ECF volume expansion
mannitol can cause Extracellular
volume expansion, what is the effect
Mannitol is distributed to extracellular space extracts water
from cells, leading to an expansion of extracellular volume hyponatremia before mannitol produces a diuresis
This can complicate heart
failure produce pulmonary edema
s/e Dehydration,
hyperkalemia hypernatremia
These side effects can result from use of mannitol without adequate water replacement
s/e Headache,
nausea vomiting
are commonly
observed
can cause thrombosis/pain from extravasation
urea
true or false
do not give to pts with impaired liver function because of risk of elevation of blood ammonia levels
true
glycerin
is metabolized can cause
hyperglycemia
mannitol
& urea
Contraindicated in active cranial bleeding
osmotic diuretics ContraIndicated in
anuric pts who are unresponsive
to test doses of ODs
