Review Question - QID 210870

A 50-year-old woman presents to her primary care physician for muscle weakness. Her symptoms have progressively worsened over several months, and she has experienced difficulty getting up from a chair, climbing the stairs, and placing her groceries on the top shelves of her kitchen. She also reports feeling tired lately and is unsure when this began. Her temperature is 98.5°F (36.9°C), blood pressure is 137/88 mmHg, pulse is 90/min, respirations are 12/min, and oxygen saturation is 98% on room air. Physical examination is notable for muscle weakness in the deltoids and hip flexors with 2+ biceps, triceps, patellar, and ankle tendon reflexes. Laboratory testing demonstrates a creatine kinase level of 4,200 U/L (normal is 10-70 U/L), lactate dehydrogenase level of 150 U/L (normal is 45-90 U/L), and thyroid-stimulating hormone level of 1.5 µU/mL (normal is 0.5-5.0 µU/mL). Which of the following is the most appropriate initial treatment for this patient?