REN and bacterial urinary tract infection: Urinary tract infection (UTI) is the most common bacterial infection in older adults.1 Trimethoprim is a first-line antibiotic prescribed in the UK for acuteuncomplicated UTI.2 Trimethoprim reduces potassium excretion in the distal nephron, which can cause elevated potassium levels.3 This is of particular importance in older adults, who are more likely to have comorbidities requiring prescription of additional medicines that may predispose them to hyperkalaemia, such as renin-angiotensin antagonists (RAA).