A 69-year-old woman visits her primary care provider because of facial asymmetry that started yesterday. She felt fine and went to bed, hoping it would go away, but it is getting worse today. She has no difficulty speaking, weakness, or numbness in her arms or legs. Her chronic medical problems include type 2 diabetes mellitus, which is well controlled with metformin. On examination, she has difficulty completely closing her right eyelid tightly; there is no sensory loss of pain, temperature, or crude. There is a loss of forehead wrinkling on the right side. The neurological examination is otherwise unremarkable. What is the best initial treatment for this pat