A 38-year-old woman with bipolar disorder started haloperidol 10 days ago for a manic episode. She now reports that she cannot sit still, repeatedly walks around the consulting room and feels driven to move her legs, although she says the mania is improving. She has developed thoughts that she would rather not be alive because the sensation is unbearable. There is no rigidity, fever or altered consciousness. Which one of the following is the most appropriate management?