CARDIO + RENAL: POTASSIUM SPARING DIURETICS

Question 1

POTASSIUM-SPARING DIURETICS: INDICATIONS

Answer 1

As part of combination therapy, for the treatment of hypokalaemia arising from loop- or thiazide-diuretic therapy.

Aldosterone antagonists (e.g. spironolactone) also have a potassium-sparing effect, and may be used as an alternative

Question 2

POTASSIUM-SPARING DIURETICS: MOA

Answer 2

• Potassium-sparing diuretics such as amiloride are relatively weak diuretics alone.
• In combo with another diuretic, they can counteract potassium loss and enhance diuresis
• Amiloride acts on the distal convoluted tubules in the kidney. It inhibits the reabsorption of sodium (and therefore water) by epithelial sodium channels (ENaC), leading to sodium and water excretion, and retention of potassium.
• This counteracts the potassium losses associated with loop- or thiazide-diuretic therapy.

Question 3

POTASSIUM-SPARING DIURETICS: ADVERSE EFFECTS

Answer 3

• GI upset
• When used in combo with other diuretics, dizziness, hypotension and urinary symptoms
• As combined preparations, electrolyte disturbances should cancel each other out, but the risk of hypokalaemia, hyperkalaemia and hyponatraemia should not be ignored.

Question 4

POTASSIUM-SPARING DIURETICS: WARNINGS

Answer 4

• Severe renal impairment and hyperkalaemia
• Combo therapy should not be started in the context of hypokalaemia
• Avoid in states of volume depletion

Question 5

POTASSIUM-SPARING DIURETICS: INTERACTIONS

Answer 5

• Do not use in combination with other potassium-elevating drugs, including potassium supplements (oral or IV) and aldosterone antagonists, due to the risk of hyperkalaemia
• As with other diuretics, renal clearance of drugs including digoxin and lithium may be altered, requiring dose adjustment.

Question 6

POTASSIUM-SPARING DIURETICS: EXAMPLES

Answer 6

• amiloride (as co-amilofruse, co-amilozide)