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.

At low aspirin doses (75–100 mg for cardioprotection), the clinical effect is minimal. At full anti-inflammatory doses, furosemide-induced diuresis drops markedly – titrate furosemide clinically or temporarily withhold aspirin during decompensation.