A middle-aged woman with hyperthyroidism received irregular drug treatment for 2 years. One week after switching to radioactive 131I therapy, she suddenly developed high fever and palpitations. Physical examination: temperature 40°C, heart rate 160/min, atrial fibrillation, tachypnea, profuse sweating, and restlessness. Lab tests: elevated WBC, neutrophilia, increased FT3 and FT4, decreased TSH. What is the treatment principle?