RENAL + GU: DIURETICS, POTASSIUM-SPARING

Question 1

DIURETICS, POTASSIUM SPARING: INDICATIONS

Answer 1

• Tx of Hypokalaemia arising from LOOP/THIAZIDE-DIURETIC Therapy
• Aldosterone antagonists (e.g. spironolactone) also have a potassium-sparing effect, and may be used as an alternative

Question 2

DIURETICS, POTASSIUM SPARING: MOA

Answer 2

• Relatively weak diuretics alone
• However, in combination 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

DIURETICS, POTASSIUM SPARING: ADVERSE EFFECTS

Answer 3

• Uncommon at low doses
• GI upset can occur
• When used in combination with other diuretics, dizziness, hypotension and urinary symptoms may be problematic
• As combined preparations, electrolyte disturbances should cancel each other out, but the risk of hypokalaemia, hyperkalaemia and hyponatraemia should not be ignored

Question 4

DIURETICS, POTASSIUM SPARING: WARNINGS

Answer 4

• Severe renal impairment and hyperkalaemia
• Combination therapy should not be started in the context of hypokalaemia, as the effect on potassium may be unpredictable
• As with all diuretics, they should be avoided in states of volume depletion

Question 5

DIURETICS, POTASSIUM SPARING: INTERACTIONS

Answer 5

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

Question 6

DIURETICS, POTASSIUM SPARING: EXAMPLES

Answer 6

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