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PDA Block 2 > Diuretics > Flashcards

Diuretics Flashcards

1
Q

Absorption in Proximal Tubule

A

Sodium reabsorbed with chloride isosmotically (50-75% of filtered load)
Potassium reabsorbed
Bicarbonate reabsorbed (80-90%)

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2
Q

Absorption in Ascending Limb of Loop of Henle

A

Sodium and Chloride reabsorbed (20-30%) - Active chloride reabsorption
Impermeable to water
May compensate for increased delivery of sodium from proximal tubule by increasing reabsorption
Cortical and medullary segments differ in response to diuretics

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3
Q

Absorption in Distal Tubule and Collecting Duct

A

Sodium Reabsorbed (8-9%)
Potassium Secreted
Regulation of sodium and potassium exchange by aldosterone
Permeability to water regulated by ADH

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4
Q

Vasodilators (Glomerulus)

A

Fenoldopam, dopamine, atriopeptins

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5
Q

6 Characteristics of vasodilators

A
  1. Increase RBF without increasing GFR
  2. Filtration fraction (GFR/RBF) decreases which reduces protein concentration and hydroosmotic forces
  3. Decrease in osmotic forces in peritubular capillaries allows water to leak back into tubule
  4. Greater back-leak reduces net reabsorption so sodium excretion increases
  5. Weak as diuretics due to compensatory sodium reabsorption in more distal segments
  6. Uses limited - Dopamine agonist may be used to increase RBF in shock
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6
Q

Osmotic Diuretics (MANNITOL) properties

A

Freely filtered
Not reabsorbed
Metabolically inert

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7
Q

Osmotic Diuretics mechanism of action

A
  • Non-reabsorbed solute limits the reabsorption of water from the tubule
  • Sodium is reabsorbed without water. Sodium concentration in tubule falls
  • Reduced sodium concentration diminishes sodium reabsorption due to unfavorable concentration gradient
  • Action continues in ascending limb and distal tubule to limite sodium reabsorption
  • Enhanced potassium excretion occurs in distal tubule due to increased sodium
  • Urine flow increases as does excretion of sodium, potassium and chloride
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8
Q

Osmotic Diuretics Therapeutic Use

A
  • Must be given intravenously - limited to inpatients
  • Acute renal failure
  • Edematous conditions in which volume load is not detrimental
  • Glaucoma
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9
Q

Toxicity or Side Effects of Osmotic Diuretics

A

Related to volume overload and expansion of intravascular fluid volume
Rare hypersensitivity

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10
Q

Drug that inhibits Carbonic Anhydrase

A

Acetazolamide

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11
Q

Mechanism of Acetazolamide

A
  • Secreted into proximal tubule by Organic Anion Transporter
  • Carbonic anhydrase catalyzes formation of carbonic acid from CO2 and H2O - this process H+ needed for bicarbonate reabsorption
  • Blockade of enzyme decreases bicarbonate reabsorption and thereby sodium reabsorption in proximal tubule - Urine pH increases
  • Loop of Henle is not permeable to bicarbonate so cannot compensate for increased sodium load
  • Potassium secretion in distal tubule increases
  • Urine volume increases as does excretion of sodium, potassium and bicarbonate
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12
Q

Therapeutic uses of Carbonic Anhydrase inhibitors

A

Glaucoma - reduce aqueous humor formation
Alkalinzine urine to decrease drug toxicity
Treat symptoms of acute altitude sickness

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13
Q

Acetazolamide Toxicity

A

Metabolic acidosis occurs which reduces renal response to the drug
Generally safe

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14
Q

Loop Diuretics

A

Furosemide
Bumetanide
Ethacrynic acid

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15
Q

Loop Diuretics Mechanism of Action (it does a lot)

A
  • Secreted into proximal tubule by OAT
  • Act on cortical and medullary segments of the ascending limb to inhibit active chloride reabsorption - results in reduced reabsorption of both sodium and chloride (NA+, K+, 2Cl- symporter)
  • In high doses may inhibit carbonic anhydrase
  • Potent diuretics, 20-30% of filtered load of sodium is excreted
  • Increases RBF and sometimes GFR
  • K+ excretion increases due to increased sodium delivery to distal tubule
  • Impairs the kidney’s ability to make a concentrated or diluted urine
  • Enhance urate reabsorption in proximal tubule
  • Enhance excretion of calcium
  • Urine volume increases as does the excretion of sodium, chloride and potassium
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16
Q

Therapeutic uses of Loop Diuretics

A
  • Diuresis is rapid in onset and short in duration
    Management of edema due to cardiac, hepatic or renal disease
  • Since loop diuretics tend to increase RBF and GFR, they are of value in treating edema associated with nephrotic syndrome and chronic renal failure
  • Acute pulmonary edema
  • Hypertension
17
Q

Loop Diuretics Toxicity

A
  • Hypokalemia
  • Hyperuricemia
  • Hyperglycemia (Furosemide)
  • Ototoxicity - deafness with high doses
  • Volume depletion
18
Q

Thiazide and Related Diuretics

A

Chlorothiazide
Hydrochlorothiazide
Metolazone

19
Q

Thiazide Diuretics Mechanism of Action

A
  • Secreted in proximal tubule by OAT
  • Act on the cortical diluting segment of ascending limb to inhibit sodium chloride reabsorption (co-transporter)
  • In higher doses, some thiazides inhibit carbonic anhydrase and have a proximal tubular effect
  • Intermediate activity - 8-10% of the filtered load of sodium excreted
  • Reduce GFR
  • Potassium secretion increases due to increased sodium delivery to distal tubule
  • Impairs the kidney’s ability to produce a dilute urine
  • Enhance urate reabsorption in proximal tubule
  • Decrease renal excretion of calcium
  • Urine volume increases as does the excretion of sodium, chloride, and potassium - hypertonic urine
20
Q

Thiazide diuretics - Therapeutic Uses

A
  • Diuresis is rapid in onset (w/in 1 hour) and long in duration
  • Management of edema due to congestive cardiac failure
  • Hypertension
  • Management of hypercalciuria in patients with renal calculi (kidney stones) composed of calcium salts
21
Q

Thiazide diuretics Toxicity

A

Hypokalemia
Hyperuricemia
Hyperglycemia - decreased insulin secretion
Should not be used when GFR < 25 ml/min

22
Q

Potassium Sparing diuretics

A

Spironolactone; Eplerenone

23
Q

K+ sparing diuretics - mechanism of action

A
  • Acts on distal tubule as a competitive antagonist of aldosterone
  • Requires endogenous aldosterone for activity
  • Urine volume increases - excretion of sodium increases; potassium excretion decreases
  • Weak as diuretics - 2-3% of filtered sodium is excreted
24
Q

K+ sparing diuretics - therapeutic uses

A
  • Hypertension
  • Refractory edema
  • Primary aldosteronism
  • Used with a thiazide or loop diuretic to enhance diuretic effect and reduce potassium loss
  • Long duration of action
25
Q

K+ sparing diuretics - Toxicity

A 
Hyperkalemia
Gynecomastia (male breasts) (Spironolactone >>>> Eplerenone)
26
Q

Sodium Channel Inhibitors

A

Triameterene

Amiloride

27
Q

Sodium Channel inhibitors - Mechanism of Action

A
  • Inhibit the entry of sodium into the principal cells - sodium potassium exchange does not occur (Amiloride works in higher concentration)
  • Effects are independent of aldosterone
  • Urine volume increases - urinary excretion of sodium increases while potassium excretion falls
  • In high doses, triamterene reduces GFR
  • Weak as diuretics (2-3% filtered sodium is excreted)
28
Q

Sodium channel inhibitors - therapeutic uses

A

Used with thiazide or loop diuretic to enhance diuretic effect and reduce potassium loss
Treatment of edema or hypertension

29
Q

Sodium Channel inhibitors - Toxicity

A

Hyperkalemia - should not be given with potassium supplements
Azotemia - Mild

30
Q

Factors for choice of diuretic (6)

A
  1. Intrinsic activity: loop > thiazides > K+ sparing
  2. Cost: thiazides > loop > K+ sparing
  3. Route of administration: IV vs. oral
  4. Speed of onset - loop > thiazides
  5. Risk to benefit ratio
  6. Effects on renal hemodynamics
31
Q

Compartmentalization of fluids

A
  • Dictates rate of fluid mobilization
  • Determine volume status
  • Diuresis derives fluid from intravascular space first, edematous tissues second and body compartments 3rd
32
Q

Electrolyte imbalance: Potassium

A
  • Potassium loss parallels sodium excretion
  • Increase intake with potassium supplements or decrease output with K+ sparing diuretics
  • Remember hyperkalemia may be fatal whereas hypokalemia is rearely life threatening
33
Q

Therapeutic use of diuretics

A

Hypertension - increase salt and water excretion and reduce ECF volume; cardiac output is reduced initially and returns to normal as peripheral resistance falls
CHF - Reduce fluid volume and end-diastolic filling pressure or preload
Edema - imbalance of starling forces

34
Q

Hydrochlorothiazide and Furosemide in antihypertensive therapy

A

Used alone to treat mild HTN
Used in combination with other antihypertensive drugs
- Prevent salt and water retention and edema caused by other antihypertensive drugs
- Enhance antihypertensive activity of other antihypertensive drugs

35
Q

Furosemide and thiazides in CHF

A

Do not improve surfival from CHF so used in combination with other drugs that do improve survival

36
Q

Spironolactone and Eplerenone in CHF

A

Inhibit renal and cardiac effects of aldosterone
Act on heart to inhibit cardiac hypertrophy and fibrosis caused by aldosterone
Prove to improve survival from CHF

37
Q

Furosemide and Thiazide diuretics in Edema

A

Increase salt and water excretion and reduce the extracellular fluid volume decreasing edema

38
Q

What causes a decrease in plasma oncotic pressure

A

Malabsorption
Nephrotic syndrome
Liver failure
Malnutrition

39
Q

What causes an increase in capillary hydrostatic pressure

A 
Venous obstruction
Cirrhosis
CHF
Constriction/restriction
Renal failure
Pregnancy

PDA Block 2 (15 decks)

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