A 17-year-old female presents with palpitations and hyperhidrosis for 6 months. Over the past month, she developed polydipsia and polyuria. Physical examination reveals significant weight loss, mild exophthalmos, grade II thyroid gland enlargement, and vascular bruit audible at both upper poles. Lab results: FT<sub>3</sub> 33.5 pmol/L, FT<sub>4</sub> 40 pmol/L, TSH 0.01 mU/L (0.01 μIU/mL). Which treatment is most appropriate for this patient's hyperthyroidism?