Furosemide × Losartan

Losartan (ARB) reduces aldosterone synthesis and angiotensin-dependent constriction of glomerular afferent arterioles. In a volume-depleted patient on a loop diuretic, the first losartan dose can sharply lower glomerular blood flow and trigger acute kidney injury.

Sharp blood pressure drop on the first dose: dizziness, syncope. Reduced urine output, rising creatinine. Weakness and paraesthesia from hyperkalaemia.

The combination is standard in hypertension and heart failure. Before starting losartan, confirm there is no dehydration (after intensive diuretic therapy). Take the first dose in the evening, lying down. Check potassium and creatinine at 1 week.