3 - Diuretics Flashcards
Which drugs are thiazide diuretics?
- Hydrochlorothiazide
- Chlorthalidone
- Metolazone
Which drug are loop diuretics?
- Furosemide
- Ethacynic acid
Which drug is a potassium sparing diuretic?
Spironolactone
What is the aim of therapy w/ diuretics?
Decrease sodium reabsorption by a few %
What would happen if Na reabsorption drops to 95%?
1250 mmol/day of Na is excreted, so 9 litres of extracellular fluid is lost
What are the functions of the proximal tubule and which drug works against each function?
- Reabsorbs filtrate water and electrolytes (mannitol, unreabsorbed glucose)
- 100% of glucose reabsorbed (dapaglifozin)
- 85% of bicarbonate reabsorbed (acetazolamide)
What is the function of the ascending loop of Henle and which drug works against this function?
- Na, K, Cl co-transported and Ca and Mg follow (reabsorbed)
- Furosemide
What is the function of the distal tubule and which drug works against this function?
- Na/Cl reabsorbed, calcium excreted
- Metolazone
Is water reabsorbed in the ascending loop of Henle?
No
Is water reabsorbed in the distal tubule?
No
What are the function of the collecting ducts and which drugs work against these functions?
- Aldosterone increase Na reabsorption and increases K and H excretion (spironolactone)
- ADH (vasopressin) increases water permeability and reabsorption (conivaptan)
Where do thiazide diuretics work?
- Distal tubule to increase NaCl excretion and decrease Ca excretion
- Some proximal tubule affect (only important when combined w/ loop diuretics)
What are the uses of thiazide diuretics?
- Edema (heart failure, liver cirrhosis)
- Hypertension
What are some disadvantages to thiazide diuretics?
- Increases incidence of other risk factors for CV disease (hyperglycemia, increase LDL levels)
- Increases incidence of erectile dysfunction
- Plasma volume contraction due to increased volume loss
What are advantages to thiazide diuretics?
- Orally active
- Low toxicity
- No postural hypotension
How are loop diuretics administered?
Orally and IV
What are the functions of loop diuretics?
- Increase prostaglandin production in nephron
- Increases Na, Cl, and K excretion and Mg, Ca follow (excreted)
- Inhibits renal diluting ability and abolishes renal concentrating ability (urine becomes isotonic and slightly dilute)
____ may decrease function of loop and thiazide diuretics
NSAIDs
What are some problems w/ loop diuretics?
- Deafness
- Chronic dilutional hyponatremia
What should loop diuretics never be combined w/?
Aminoglycoside antibiotics
What are loop diuretics used for?
- Renal insufficiency
- Edema (pulmonary)
- Hypertension (not as sole medication)
- Hypercalcemia
- Heart failure
What should be done if px not responding to a loop diuretic?
- Caution regarding circulating chloride concentration
- Add thiazide diuretic
Thiazide and/or loop diuretics can cause _____ depletion
Potassium
When is potassium depletion a concern w/ thiazide and loop diuretics?
If low potassium is already a problem (ex: heart failure, cirrhosis)
What are the 2 main causes of potassium depletion from thiazide and loop diuretics?
1) Secondary hyperaldosteronism (increased renin = increased A2 = increased aldosterone => Na reabsorption and K loss)
2) Increased distal delivery (Na reabsorption inhibited in loop and distal tubule, so collecting tubules increase Na reabsorption)
What is the tx for potassium depletion?
1) Dietary intake (apricots, bananas)
2) Potassium chloride tablets
3) Emergencies = IV KCl
4) Potassium sparing diuretics (given w/ other diuretics to decrease K loss)
Rank the 3 types of diuretics from strongest to weakest at removing sodium
Loop > thiazide > potassium sparing
What are the functions of spironolactone?
- Blocks aldosterone receptor
- Prevents cardiac remodelling, so may delay progression of heart failure
What is the function of triamterene?
Decreases sodium permeability
What effect do beta antagonists, ACE inhibitors, and ARBs have on plasma potassium concentrations?
May increase concentrations
What can cause extracellular volume depletion? What are ways to overcome these?
- Inability to concentrate urine/save water - drink more water to excrete solutes
- Inability to dilute urine/excrete excess urine - ingest hypotonic solution to excrete isotonic urine
What effect does furosemide have on extracellular volume depletion?
Makes the kidney unable to concentrate or dilute urine
What effect do diuretics have on calcium?
- Thiazides decrease calcium excretion (good for hypocalciuria)
- Furosemide increases calcium excretion
What effect do diuretics have on uric acid excretion?
Initially increased, but decreased w/ chronic administration
What do diuretics have on lithium?
Increased proximal tubular reabsorption
Which type of diuretic is preferred for tissue edema?
Loop diuretic
What is the first line single therapy for hypertension?
Thiazide diuretic
Why are diuretics used for heart failure?
Fluid retention increases vascular volume, and diuretics decrease vascular volume
