Summary

A 69-year-old man presented to the emergency department with lower respiratory tract infection and febrile neutropaenia. He was recently discharged following a 50-day hospital stay with newly diagnosed microscopic polyangiitis, complicated by pulmonary haemorrhage and severe renal dysfunction requiring renal replacement therapy, plasma exchange and immunosuppression (cyclophosphamide and methylprednisolone). High risk of pneumocystis pneumonia (PCP) led to an escalation in treatment from prophylactic to therapeutic oral co-trimoxazole, alongside broad-spectrum antibiotics. The patient suffered from severe and protracted hypoglycaemia, complicated by a tonic–clonic seizure 7 days after escalation to therapeutic co-trimoxazole. Endogenous hyperinsulinaemia was confirmed and was attributed to co-trimoxazole use. Hypoglycaemia resolved 48 hours after discontinuation of co-trimoxazole. PCP testing on bronchoalveolar lavage was negative. Owing to the prescription of heavy immunosuppression in patients with vasculitis and the subsequent risk of PCP warranting co-trimoxazole prophylaxis, we believe that the risk of hypoglycaemia should be highlighted.