Diuretics and Aquaretics Flashcards
What is the main goal/purpose of diuretic use?
to moblilze or get rid of Na+
What does potency of a diuretic refer to?
The extent to which they moblize Na+ (more potent=more Na+ loss in urine)
Which diuretic classes act predominantly in the PCT? (2)
- CA Inhibitors 2. Osmotic Diuretics
Which diuretics act along the L of H?
Loop Diuretics
Which diuretic classes act predominantly in the DCT? (3)
Thiazide Diuretics, Aldosterone Antagonists, K-Sparing Diuretics
What are the two major areas of the nephron where CA is present and in what relative amounts?
- 90% in PCT
2. 10% in DCT
What is a specific CA Inhibitor?
Acetazolamide
What is the mechanism of action of CA inhibitors?
They are potent competitive inhibitors of CA, acting in PT (90%) and DT (10%), resulting in bicarbonate loss in the urine (as H+ needed for HCO3- reabsorption is not produced)
What is the net effect of CA inhibitor use? (2)
- Alkaline urine
2. Enhanced chloride reabsportion (leading to hyperchloremic systemic acidosis)
Clinical uses of CA Inhibitors? (4)
- In Glaucoma to reduce intraocular pressure
- To alkalinize tubular urine in patients with Cystinuria
- Management of seizures
- Prophylaxis for mountain sickness
Side effects of CA inhibitors? (2)
- Metabolic Acidosis
2. Markedly increases K+ loss in urine for one day (acute hypokalemia bc MD goes crazy)
What are the characteristics of Osmotic Diuretics (4)? One example?
Small (1) molecules that are filtered (2) but not reabsorbed (3) by the kidney; they are inert (4) (have no other pharmacologic effect; Example→Mannitol
What is the mechanism of action of Osmotic Diuretics? What two places do they effect?
- PCT (minor)→They osmotically inhibit Na+/H20 reabsorption in the PCT.
- Loop (major)→They expand ECFV by increasing plasma osmolarity (decreased blood viscosity as water is drawn out of peripheral tissues)→ increase renal medullary blood flow→ reduces the medullary tonicity→impairs the ability of thin segments of L of H to extract H2O and reabsorb NaCl
Net effect of Osmotic Diuesis use?
- Significantly increase urine flow and volume with small increments of Na+, K+, and Cl-
- Initially increases plasma volume and BP
Clinical uses of Osmotic Diuretics? (3)
- Treatment of Dialysis Disequilibrium Syndrome
- Reduce Intracranial Pressure
- Reduce Intraocular Pressure
Side effects of OD’s? (2)
- Volume Overload
2. Contraindicated in patients with heart failure (may not be able to tolerate the volume expansion)
What is the mechanism of action and effect of Loop Diuretics?
Inhibit Na-K-2Cl symporter in TALH and the ability of MD to sense NaCl.
Increase RBF
Increase Prostaglandin biosynthesis
Stimulate renin release and maintain GFR
What are the three ways that LD’s increase renin release inside the kidney?
- Inhibiting the MD
- Reflexively activating the sympathetic NS
- Stimulating intrarenal baroreceptor mechanisms
Net effects of LD use? (3)
- Copious diuresis with significant Na loss
- Increase K+, Ca2+, and Mg2+ excretion
- Increased excretion of H+ resulting in mild metabolic alkalosis
STAR: Impairs ability of kidney to concentrate urine, resulting in copious diuresis while maintaining GFR
What are three examples of LD’s?
Furosemide (Lasix), Bumetanide, Torsemide
Therapeutic uses of LD’s? (6)
- Moderate to severe Edema or HTN due to cardiac, hepatic, and/or renal failure (GFR<30ml/min)
- Acute pulmonary edema→rapid mobilization of edema fluid
- Mobilization of Ca2+ in hypercalcemia
- Maintenance of renal PGs, renin, and GFR to prevent renal failure
- Wash out toxins by increasing urine flow
- Antihypertensive particularly when GFR is very low (often in combo with other drugs)
What effects allow LD’s to aid in the treatment of Acute pulmonary edema? (4)
Decrease Pulmonary wedge pressure, Venodilation resulting in reduced LV filling pressure, Increased compliance of pulmonary vasculature that facilitates mobilization of fluids, Brisk copious diuresis
What is the most potent class of diuretics?
Loop Diuretics
What is required for Furosemide to be able to inhibit the luminal NK2C symporter?
It must first be secreted into the lumen by organic acid transporters in the PCT into the lumen.
Dose-response curve of Furosemide is shifted to the right by what?
Renal disease (impaired secretion); in patients with renal disease and reduced GFR, the dose has to be increased from 20 (normal) to 200 mg/day.
Is it ok to dramatically increase the amount of Furosemide given to patients with Renal disease and low GFR? Why?
Yes; because it has a wide margin of safety (TI; the minimum beneficial concentration is much lower than the MTC)
What are the side effects of Furosemide?
- Fluid and electrolyte imbalance (hypokalemia and pH disorders, mostly alkalosis)
- Ototoxicity (dont give with streptomycins which have this same effect)
- Elevated BUN, Hyperglycemia, Hyperuricemia
- Drug interactions
What are some drug interactions of furosemide?
- Li+ 2. Indomethacin (NSAIDs which reduce effectiveness by inhibiting PG synthesis) 3. Probenecid (impairs secretion)
- Warfarin
Why is furosemide contraindicated in patients taking warfarin?
Warfarin is 99% protein bound, while Furosemide is 80% protein bound. Furosemide could displace warfarin, drastically increasing its therapeutic levels, resulting in bleeding.
Which LD is taken instead of furosemide in patients taking warfarin?
Bumetanide (40x more potent than furosemide)
What does torsemide do? How is it different than other LD’s (2)?
It’s a vasodilator:
- It’s a long-lasting LD (given once daily; longer half-life)
- In addition to diuretic effect, it also lowers blood pressure
How much of the GFR is handled in the DCT? What happens to the tubular fluidin the DCT?
Only 10% of GFR is handled in DCT, where fine-tuning of urinary volume and composition takes place.
What are the three different segments in the DCT?
- Na-K Aldosterone-Independent segment (has Na-Cl symporter; Na reabs without H2O reabs)
- Aldosterone-Sensitive segment (Na exch’d for H+ and K+)
- Sodium Load Segment (Na reabs is proportional to amt of Na that reaches this segment in exch for H+ and K+)
How much of the Na+ filtered is absorbed in the inner medullary CD and what two types of Na+ channels are expressed in IMCD?
Up to 5%; 1. Amiloride-sensitive cyclic nucleotide gated (CNG) cation channel 2. Low-conductance highly selective ENaC channel
What is the other name for Thiazide Diuretics (TDs) and what are some specific examples?
Benzothiadiazides;
1. Hydrochlorothiazide (HCTZ) 2. Chlorthalidone 3. Metolazone (4. Quinethazone 5. Indapamide)
What is the mechanism of action of TD’s?
They inhibit Na-Cl symporter in the aldosterone-independent segment of the early DCT.
What is the net effect of TD use? (4)
- Mild loss of Na+ and water
- Na+ loss leads to reduced GFR (w/ chronic use)
- Elevated K+ excretion→Hypokalemia
- Increased H+ excretion (as titratable acid HCl)→Hypochloremic Alkalosis
How do TD’s compare to LD’s in excretion of Mg2+ and Ca2+
LD’s increase urinary excretion of both, while TD’s increase urinary excretion of Mg2+ but decrease urinary excretion of Ca2+