Every day your kidneys filter something like 180 litres of blood, sieving out waste while clinging to the things your body wants to keep. When that machinery starts to fail, it rarely does so loudly. Protein begins leaking into the urine, the filtration rate creeps downward, and the slide, once it starts, tends to keep going. For a huge slice of patients, doctors have had little to throw at that slide beyond the standard blood-pressure pills. Until now, perhaps. A drug called finerenone,...