diuretic therapy
DESCRIPTION
terapi farmakologi obat golongan diuretikTRANSCRIPT
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Diuretic TherapyIn Cardiovascular Disease
Saepudin, S.Si., M.Si., Apt.
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• Diuretics increase the rate of urine flow and sodium excretion
• They are used to adjust the volume and/or composition of body fluids in a variety of clinical situations hypertension, heart failure, renal failure, nephrotic syndrome, and cirrhosis
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Introduction • Diuretics remain important tools in
therapy for cardiovascular diseases• They are capable of reducing blood
pressure, while simultaneously decreasing the morbidity and mortality that attends the hypertensive state
• Diuretics are currently recommended as first-line therapy for the treatment of hypertension by the JNC
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Individual classes of diuretics• Carbonic anhydrase inhibitors• Loop diuretics• Thiazides• Potassium-sparing diuretics• Osmotic diuretics
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General mechanism• By definition, diuretics are drugs that
increase the rate of urine flow• However, clinically useful diuretics also
increase the rate of excretion of Na+ (natriuresis) and of an accompanying anion, usually Cl-
• NaCl in the body is the major determinant of extracellular fluid volume, and most clinical applications of diuretics are directed toward reducing extracellular fluid volume by decreasing total-body NaCl content
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General mechanism• Although continued administration of a
diuretic causes a sustained net deficit in total-body Na+, the time course of natriuresis is finite renal compensatory mechanisms (diuretic braking )
• These mechanisms include activation of the SNS, activation of the RAA axis, decreased arterial BP, hypertrophy of renal epithelial cells, increased expression of renal epithelial transporters, and perhaps alterations in natriuretic hormones such as ANP
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Nephron Structure
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Renal Epithelial Cell Polarity Drives Na+ and Water Transport
Tubular Fluid
Blood
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Proximal Tubule
• Na+ flows down concentration gradient
• Na/K ATPase maintains gradient• Water follows passively• 67% of Na and water reabsorption
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Loop of Henle• TDL permeable to water but not Na+
• TAL impermeable to water and transports Na+
• Differences in permeabilities creates the countercurrent multiplier
• Countercurrent multiplier creates interstitial osmolar gradient
• 20% of filtered load of Na absorbed by the TAL
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Distal Convoluted Tubule
• 5% of filtered load of Na+ reabsorbed• Segment mostly impermeable to water
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Cortical Collecting Duct• Water permeability controlled by
antidiuretic hormone (ADH)• Driving force for water reabsorption is
created by the countercurrent multiplier• 2-3% of filtered Na+ reabsorbed here via
Na+ channels that are regulated by aldosterone
• Major site of K+ secretion
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Several important principles• When a diuretic interferes with the
reabsorption of Na at any site of tubule, it results in inhibition of other renal functions related to reabsorption of Na at that site
• In other words, interference with Na reabsorption in the PT leads to increase delivery of NaCl to TAL and DT creation of free water and increase K loss
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Several important principles• Diuretics act only if Na reachs their site of
action• More distally acting diuretics lose their
effectiveness if proximal sodium reabsorption is increased
• Diuretics acting at different sites or at the same site by different mechanism may be additive or sinergistic can be used to great clinical advantage
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Definitions• Diuretic : substance that promotes the
excretion of urine• Natriuretic : substance that promotes the
renal excretion of sodium
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Class of Diuretics• Thiazide diuretics
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Thiazide Action
• Thiazides freely filtered and secreted in proximal tubule• Bind to the electroneutral NaCl cotransporter• Thiazides impair Na+ and Cl- reabsorption in the early
distal tubule: “low ceiling”
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Increased K+ Excretion Due To:• Increased urine flow per se• Increased Na+-K+ exchange• Increased aldosterone release
Na+/K+ exchange in the cortical collecting duct
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Whole Body Effects of Thiazides
• Increased urinary excretion of:– Na+
– Cl-
– K+
– Water– HCO3
- (dependent on structure)
• Reduced ECF volume (contraction)• Reduce blood pressure (lower CO)• Reduced GFR
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Pharmacokinetics
• Oral administration - absorption poor• Diuresis within one hour• T1/2 for chlorothiazide is 1.5 hours,
chlorthalidone 44 hours
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Therapeutic Uses
• Edema due to CHF (mild to moderate)• Essential hypertension• Diabetes insipidus• Hypercalciuria
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Therapeutic use• Not only are thiazides usually effective when
given once daily as monotherapy also have additional benefit when combined with most antihypertensive drugs
• Typically, about 50% of patients will have a good blood pressure response to monotherapy with a low dose
• Poor responders tend to have a more marked augmentation in aldosterone concentration
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Diabetes Insipidus• Thiazides: paradoxical reduction in urine volume• Mechanism: volume depletion causes decreased
GFR• Treatment of Li+ toxicity:
– Thiazides useful– Li+ reabsorption increased by thiazides. Reduce
Li dosage by 50%
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Thiazide Use in Hypercalciuria - Recurrent Ca2+ Calculi
• Thiazides promote distal tubular Ca2+ reabsorption
• Prevent “excess” excretion which could form stones in the ducts of the kidney
• 50-100 mg HCT kept most patients stone free for three years of follow-up in a recent study
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Thiazide Toxicity• Hypokalemia due to:
– Increased availability of Na+ for exchange at collecting duct
– Volume contraction induced aldosterone release • Hyperuricemia
– Direct competition of thiazides for urate transport– Enhanced proximal tubular reabsorption efficiency
• Hyperglycemia– Diminished insulin secretion– Related to the fall in serum K+
• Elevated plasma lipids
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Class of Diuretics
Loop diuretics• More efficacious than the thiazides
greater risk of hypovolemia• For treatment of hpertension thiazides are
preferable and actually more efficacious compared with loop diuretics
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Available Loop Diuretics
• Furosemide (prototype)
• Bumetanide• Torsemide• Ethacrynic acid
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Molecular Mechanism of Action
• Enter proximal tubule via organic acid transporter
• Inhibition of the apical Na-K-2Cl cotransporter of the TALH
• Competition with Cl- ion for binding
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Pharmacological Effects of Loop Diuretics
• Loss of diluting ability: Increased Na, Cl and K excretion
• Loss of concentrating ability: – reduction in the medullary osmotic gradient – Loss in ADH-directed water reabsorption in
collecting ducts• Loss of TAL electrostatic driving force:
increased excretion of Ca2+, Mg2+ and NH4+
• Increased electrostatic driving force in CCD: increased K+ and H+ excretion
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Pharmacokinetics• Rapid oral absorption, bioavailability ranges
from 65-100%• Rapid onset of action • extensively bound to plasma proteins• secreted by proximal tubule organic acid
transporters
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Therapeutic Uses
• Edema of cardiac, hepatic or renal origin• Acute pulmonary edema – (parenteral route)• Chronic renal failure or nephrosis• Hypertension • Symptomatic hypercalcemia
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Therapeutic use• Furosemide is used at doses of 20 mg and
upward• Renal insufficiency need higher doses• Furosemide should be used in divided
doses of two or more per day duration of diuretic action may be qiute short and is likely dose-related
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Loop Diuretic Toxicity• Hypokalemia• Magnesium depletion• Chronic dilutional hyponatremia• Metabolic alkalosis• Hyperuricemia• Ototoxicity
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Drug Interactions• Displacement of plasma protein binding of
clofibrate and warfarin• Li+ clearance is decreased• Loop diuretics increase renal toxicity of
cephalosporin antibiotics• Additive toxicity w/ other ototoxic drugs• Inhibitors of organic acid transport (probenecid,
NSAID's) shift the dose-response curve of loop diuretics to the right
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Spironolactone• Mechanism of action:
aldosterone antagonist• Aldosterone receptor
function• Spironolactone prevents
conversion of the receptor to active form, thereby preventing the action of aldosterone
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Pharmacokinetics• 70% absorption in GI tract• Extensive first pass effect in liver and
enterohepatic circulation• Extensively bound to plasma proteins• 100% metabolites in urine• Active metabolite: canrenone (active)• Canrenoate (converted to canrenone)
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Therapeutic Uses• Prevent K loss caused by other diuretics
in:– Hypertension– Refractory edema– Heart failure
• Primary aldosteronism
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Administration
• Dose orally administered (100 mg/day)• Spironolactone/thiazide prep (aldactazide, 25
or 50 mg of each drug in equal ratio)
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Toxicity• Hyperkalemia - avoid excessive K
supplementation when patient is on spironolactone
• Androgen like effects due to it steroid structure• Gynecomastia• GI disturbances
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Triamterene and Amiloride
• Non-steroid in structure, not aldosterone antagonists
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Mechanism of Action• Blockade of apical Na+
channel in the principal cells of the CCD
• Amiloride: blocks the Na/H exchanger (higher concentrations)
• Blockade of the electrogenic entry of sodium causes a drop in apical membrane potential (less negative), which is the driving force for K+ secretion
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Pharmacokinetics• Triamterine
– 50% absorption of oral dose– 60% bound to plasma proteins– Extensive hepatic metabolism with active
metabolites– Secreted by proximal tubule via organic cation
transporters• Amiloride
– 50% absorption of oral dose– not bound to plasma proteins– not metabolized, excreted in urine unchanged– Secreted by proximal tubular cation transporters
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Therapeutic uses
• Eliminate K wasting effects of other diuretics in:– Edema– Hypertension
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Toxicity• Hyperkalemia. Avoid K+ supplementation• Drug interaction - do not use in combination with
spironolactone since the potassium sparing effect is greater than additive
• Caution with ACE inhibitors• Reversible azotemia (triamterine) • Triamterene nephrolithiasis. 1 in 1500 patients
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Class of Diuretics• Carbonic anhydrase inhibitors
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Acetazolamide
Developed from sulfanilamide, after it was noticed that sulfanilamide caused metabolic acidosis and alkaline urine.
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Mechanism of Action: Na+
Bicarbonate Diuresis
• Inhibit carbonic anhydrase in proximal tubule• Blocks reabsorption of bicarbonate ion,
preventing Na/H exchange• Pharmacological effect
– Sodium bicarbonate diuresis– metabolic acidosis
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Therapeutic Uses• Urinary alkalinization• Metabolic alkalosis• Glaucoma: acetazolamide, dorzalamide• As a diuretic in patients who are poorly
responsive or refractory to large doses of potent loop diuretics
• Acute mountain sickness
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CA Inhibitor Toxicity
• Hyperchloremic metabolic acidosis• Nephrolithiasis: renal stones• Potassium wasting
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Class of Diuretics• Osmotic Diuretics
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Characteristics of Osmotic Diuretics
• Freely filterable• Little or no tubular reabsorption• Inert or non-reactive• Resistant to degradation by tubules
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Mechanism of Action:Inhibition of Water Diffusion
• Free filtration in osmotically active concentration
• Osmotic pressure of non-reabsorbable solute prevents water reabsorption and increase urine volume– Proximal tubule– Thin limb of the loop of Henle
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Osmotic Diuretics in Current Use
• Mannitol (prototype)• Urea• Glycerin• Isosorbide
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Therapeutic Uses
Prophylaxis of renal failureMechanism:
• Drastic reductions in GFR cause dramatically increased proximal tubular water reabsorption and a large drop in urinary excretion
• Osmotic diuretics are still filtered under these conditions and retain an equivalent amount of water, maintaining urine flow
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• Reduction of CSF pressure and volume
• Reduction of intraocular pressure
Therapeutic Uses (Cont.)Reduction of pressure in extravascular fluid compartments
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Toxicity of Osmotic Diuretics
• Increased extracellular fluid volume• Hypersensitivity reactions• Glycerin metabolism can lead to
hyperglycemia and glycosuria• Headache, nausea and vomiting
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Summary: Sites of Diuretic Action