28. Potassium sparing diuretics, ADH antagonists, osmotic diuretics Flashcards
Where do Potassium-Sparing Diuretics work?
Works on the tubules only
List the Vasopressin I and II agonists.
- Desmopressin: Vasopressin II agonist. Used in diabetes insipidus (no pressor effect).
- Ornipressin: Vasopressin I selective agonist. Acts as a pressor, given in combo with local anesthetics to inhibit systemic absorption.
List the primarily water-excreting diuretics.
- Osmotic diuretics
- ADH-antagonists
List some osmotic diuretics.
- Mannitol
- Glycerol
- Urea
- Isosorbide
What are the indications of osmotic diuretics?
- Cerebral edema (and other ↑ ICP cases): suck water from interstitial space. cause severe dehydration.
- Acute glaucoma attack or (ophthalmological surgery - to ↓ IOP prior to surgery)
- Acute renal failure: (only early, before anuria) absolutely CI if anuric patient, also CI in cerebral trauma…can worsen cerebral edema.
What are the side effects of using osmotic diuretics?
- Dehydration
- Pulmonary edema (acutely) – because mannitol rapidly draws water into the extracellular space, by extracting from cells–>edema.
- Hyponatremia: also from drawing water into EC space.Mannitol also has late hypernatremia due to excessive diuresis without water replacement.
- Exacerbation of HF due to ↑ EC space
List the V2R antagonists.
- Tolvaptan: V2 receptor antagonist. V2 is in kidney. Used for SIADH.
- Conivaptan: both vasopressin I and II receptor ATG. V1 is in vessels and causes vasoconstriction.
What are the indications of ADH-antagonists?
- Inappropriate ADH secretion conditions.
- Refractory edemas: (cirrhosis, nephrosis, HF) - but do not ↓ mortality long-term.
What is the mechanism of action of Aldosterone antagonists?
Aldosterone antagonists inhibit aldosterone receptors → ↓ expression of aldosterone-dependent Na/K-ATPase, Na transporters (ENaC), K+ channels on principal cells and H+-ATPase on α-intercalated cells
List the Aldosterone antagonist drugs.
- Spironolactone: non-selective. also acts on progesterone, glucocorticoid, and androgen receptors.
- Canrenone: spironolactone derivative.
- Eplerenone: spironolactone derivative. selective for aldosterone receptors.
What are the indications for Aldosterone antagonist use?
-
Hyperaldosteronism:
- Primary: Conn
- Secondary: due to refractory edemas via CHF, nephrotic syndrome, liver cirrhosis; any condition with ↓ intravascular volume
- Congestive heart failure: Eplerenone is only for CHF in Europe, in the US can also be used for HTN.(Heart Failure - can ↓ myocardial remodeling/fibrosis via ↓ aldosterone effects - ↑ volume, etc.)
- Hypertension: combo with K-wasting Diuretics - especially eplerenone. should not be combined with ACE-I (would cause hyperkalemia)
- (Polycystic Ovary Syndrome / Hirsutism - spironolactone blocks 17α-hydroxylase → ↓ testosterone levels)
What are the side effects of Aldosterone antagonists?
- Significant hyperkalemia. esp combo with ACE-I, ARB or BB
- Metabolic acidosis (non-anion gap, type 4 RTA: ): ↓ aldosterone effect → ↓ H-ATPase activity. (Sketchy: “Type 4 renal tubular acidosis” - only RTA type with hyperkalemia)
- Anti-androgenic action: antagonize testosterone. in men, long treatment → gynecomastia (due to androgen receptor inhibition) + other endocrine symptoms including: impotence, reduced libido, etc.
What are the indications for direct sodium transport blocker use?
- Hypertension
- Edema: usually in combo with thiazide
- Nephrogenic Diabetes Insipidus: specifically lithium-induced NDI; blocks Li entry into collecting duct cells → ↑ clearance of Li.
- Liddle syndrome (rare AD disorder of overactive ENaC)
NOTE: These drugs are not used so much, sometimes for hypertension. Overall they are not great drugs, hopefully won’t be around much longer.
Name the direct sodium transport blockers.
- Amiloride
- Triamterene
What is the MOA of direct sodium transport blockers?
They inhibit ENaC Sodium transporter in CT principal cells → ↓ Na reabsorption + ↓ K secretion.
How are osmotic diuretics metabolized?
They cannot be metabolized..first 2 are sugar-like agents. They remain in nephron, keep water to themselves, flow through nephron and excrete water.
List the potassium-sparing diuretics.
- Aldosterone antagonists: Spironolactone, Eplerenone.
- Direct Na transporter blockers/ ENaC inhibitors: Amiloride, Triamterene.
What is the route of administration of osmotic diuretics?
Given IV infusion (otherwise would cause diarrhea).
Are osmotic diuretics strong diuretics?
They are the strongest diuretics! stronger than furosemide.
List the ADH antagonists.
- V2R antagonists: Conivaptan, Tolvaptan
- Agents that alter ADH activity: Lithium, Demeclocyclin.
What is the DOA of aldosterone antagonists?
They are known as “sneaky diuretics” because they take longer to work, but eventually work very well.
What are the indications for aldosterone antagonists?
They can treat resistant things like ascites, where furosemide doesn’t work.
Are aldosterone antagonist given by themselves or in combination therapy?
- They are usually not given alone, but with thiazide diuretics (potassium balance).
- You should be careful with ACE-I combination (hyperkalemia)
- Don’t combine potassium sparing drugs with diabetics, increase mortality.
What are the effects of Aldosterone?
- Aldosterone activates ENac (Na+ reabsorbed)
- It causes K+ excretion
- It also causes H+ excretion
What is the MOA of osmotic diuretics?
Act in whole nephron, but strongest in PCT due to free water permeability there (and descending limb). **Proximal sodium reabsorption also decreases.
