Acetylsalicylic acid × Furosemide

Dual mechanism: aspirin competes with furosemide for organic anion tubular secretion in the renal tubules (so furosemide does not reach its target in the loop of Henle lumen), and concurrently suppresses renal prostaglandin synthesis supporting glomerular perfusion.

Reduced urine output, worsening oedema, weight gain. In heart failure: dyspnoea, orthopnoea. Blood pressure and creatinine may rise.

Per the acetylsalicylic acid SmPC, when aspirin and a diuretic are given together, ensure adequate hydration and check renal function (creatinine) at the start of treatment. The risk of acute kidney injury is higher with dehydration or hypovolaemia. The same SmPC links the fall in glomerular filtration to high aspirin doses. At anti-inflammatory doses furosemide diuresis may drop: adjust the furosemide dose by weight, oedema and urine output, or withhold aspirin during decompensation. Furosemide competes with salicylates for renal excretion, so with high-dose aspirin salicylate toxicity can occur at lower doses (FDA Lasix label).