An unusual case of a 49-year-old female patient with a history of hyperthyroidism in management with mettimazole 40mg/day is presented. Quien is admitted to the ICU with a picture of febrile neutropenia secondary to agranulocytosis caused by the toxic effect of metymazole and the development of septic shock. When performing the assertive diagnosis, the drug was immediately discontinued and therapy with granulocytic colony growth factor was initiated, later the patient presents successful clinical improvement, is discharged from the ICU and continued its management in the general ward.