An association between both co-trimoxazole, or trimethoprim alone, with hyperkalaemia is well reported, particularly in association with renin-angiotensin system blockers.3, 7, 8, 30, 31, 32, 33 Our results suggest that, regardless of other drug use (renin-angiotensin system blockers or potassium-sparing diuretics), trimethoprim (but not ciprofloxacin), is associated with a more than doubling of the odds of hyperkalaemia. This evidence concerns the gene REN and Hyperkalemia.