Thiazide Diuretics · Pharmacology

Why are thiazide diuretics considered less effective in patients with a Glomerular Filtration Rate (GFR) below 30 mL/min?

  1. They are highly toxic to the damaged glomerulus
  2. They fail to reach their site of action in the tubular lumen
  3. They cause severe metabolic acidosis in renal failure
  4. They are rapidly metabolized by the liver in uremia
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Correct answer: They fail to reach their site of action in the tubular lumen

Thiazides must be secreted into the tubular lumen to work. In severe renal impairment, the delivery of the drug to the distal tubule is insufficient to produce a meaningful diuretic effect, necessitating the use of loop diuretics.

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