A 41-year-old man complains of right ear pain, difficulty closing his right eye, and drooping of the right side of his face. He finds that his right ear is sensitive to loud, low frequency sounds. When a small spoonful of sugar is applied to the right side of his tongue, he says that it tastes like sand. The physical examination identifies right-sided weakness of the upper and lower face. The patient's symptoms started 2 days ago. Which of the following is the most appropriate treatment at this time?