perindopril and spironolactone

Additive effect on potassium handling. Perindopril inhibits ACE, reducing aldosterone production and thereby increasing renal potassium retention. Spironolactone blocks aldosterone receptors in the distal nephron, further reducing potassium excretion. The combination potentiates hyperkalaemia risk.

The risk of clinically significant hyperkalaemia is increased, which can cause cardiac arrhythmias, including bradycardia and ventricular tachycardia, and may be fatal. This is particularly likely in patients with renal impairment, diabetes, or those taking other potassium-elevating drugs or potassium supplements.

Use with caution. Monitor serum potassium and creatinine within 1 to 2 weeks of starting or changing the combination, and regularly thereafter. Avoid in patients with severe renal impairment (eGFR < 30 mL/min) or baseline potassium > 5.0 mmol/L. If combined, use lower doses and consider stopping if potassium rises above 5.5 mmol/L.

This interaction is well established in clinical practice and supported by multiple guidelines and therapeutic trials, particularly in heart failure where the combination is used deliberately with monitoring. The risk of hyperkalaemia is clearly documented.