spironolactone and potassium chloride

Spironolactone, a mineralocorticoid receptor antagonist, blocks aldosterone in the distal nephron, reducing potassium excretion. Adding potassium chloride, an exogenous potassium salt, directly increases serum potassium. The combined effect of reduced renal potassium loss and increased potassium intake can lead to severe hyperkalaemia.

Hyperkalaemia can cause muscle weakness, paraesthesia, and life-threatening cardiac arrhythmias including ventricular fibrillation and asystole. Risk is greatest in patients with renal impairment, diabetes, or concurrent use of other potassium-sparing agents or ACE inhibitors.

Co-prescription is contraindicated. If the combination is considered essential, it must be used only under specialist supervision with frequent monitoring of serum potassium, electrolytes, and renal function. Stop the potassium supplement and seek immediate medical attention if hyperkalaemia develops. Consider alternative potassium-sparing strategies or non-potassium-sparing diuretics.

Well established from clinical experience, case reports, and guideline recommendations; listed as a contraindicated interaction in major reference sources such as the British National Formulary.