New research suggests that administration of co-trimoxazole in patients aged ≥66 years receiving angiotensin-converting-enzyme inhibitors or angiotensin-receptor blockers is associated with an increased risk of sudden death compared with administration of amoxicillin. In this case-controlled study, approximately three deaths within 14 days occurred per 1,000 prescriptions of co-trimoxazole. The researchers propose that this effect might be due to undiagnosed hyperkalaemia, and alternative antibiotics that do not contain trimethoprim should be considered for these patients.