USMLE (Fach) / Pharmacology - Renal (Lektion)
Urine NaCl: ↑ with all diuretics. Serum NaCl may decrease as a result.
Urine K+: ↑ especially with loop and thiazide diuretics. Serum K+ may decrease as a result.
↓ (acidemia): carbonic anhydrase inhibitors: ↓ HCO3- reabsorption. K+ sparing: aldosterone blockade prevents K+ secretion and H+ secretion. Additionally, hyperkalemia leads to K+ entering all cells in exchange for H+ exiting cells.
↑ (alkalemia): loop diuretics and thiazides cause alkalemia through several mechanisms:
- Volume contraction → ↑ AT II → ↑ Na+/H+ exchange in PCT → ↑ HCO3- reabsorption
- K+ loss leads to K+ exiting all cells (via H+/K+ exchanger) in exchange for H+ entering cells
- In low K+ state, H+ (rather than K+) is exchanged for Na+ in cortical collecting tubule → alkalosis and "paradoxical aciduria"
↑ with loop diuretics: ↓ paracellular Ca2+ reabsorption → hypocalcemia
↓ with thiazides: enhanced Ca2+ reabsorption
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