Potassium‑sparing diuretics such as spironolactone inhibit renal potassium excretion. In patients who already have elevated serum potassium, the drug can precipitate severe hyperkalemia, leading to cardiac conduction abnormalities and potentially fatal arrhythmias.
Do NOT start spironolactone in patients with serum K⁺ >5.0 mmol/L.
Monitor serum potassium and creatinine within 48 h of initiation and then weekly until stable.
Educate patients to avoid high‑potassium foods and potassium supplements.
Immediate discontinuation is required if K⁺ rises >5.5 mmol/L or if ECG changes appear.
Spironolactone antagonizes aldosterone at the distal nephron, reducing Na⁺ reabsorption and K⁺ secretion. When baseline serum K⁺ is high, the additional reduction in renal potassium excretion overwhelms compensatory mechanisms, causing a rapid rise in extracellular potassium concentration.
Marked increase in serum K⁺ (>6.5 mmol/L) can cause muscle weakness, paresthesias, and life‑threatening cardiac effects such as peaked T‑waves, widened QRS complexes, ventricular tachycardia, or asystole.
Avoid prescribing spironolactone (or other potassium‑sparing agents) in patients with documented hyperkalemia. If use is unavoidable, obtain baseline and frequent serum potassium measurements, discontinue the drug at the first sign of rising K⁺, and consider alternative diuretics (e.g., loop diuretics). Initiate potassium‑lowering therapies (e.g., sodium polystyrene sulfonate, insulin‑glucose, or dialysis) if K⁺ exceeds safe thresholds.
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