Acetylsalicylic acid × Spironolactone

Aspirin suppresses renal prostaglandin synthesis that maintains glomerular perfusion. Diuretic and natriuretic effects of spironolactone diminish and potassium accumulates.

Oedema, weight gain, rising blood pressure. Weakness, paraesthesia, and arrhythmias from hyperkalaemia. Reduced diuretic effect emerges within 1–2 weeks of starting aspirin.

At low aspirin doses (75–100 mg for cardioprotection), the clinical effect is minimal; co-prescription is acceptable with potassium and creatinine monitoring. At full anti-inflammatory doses, the diuretic response drops markedly – titrate spironolactone clinically.