A 42-year-old woman with bipolar I disorder has been on olanzapine 15 mg/day for 6 months. She presents with severe muscle rigidity, fever (39.8°C), altered mental status, and autonomic instability (HR 118/min, BP 160/95 mmHg). Serum creatine kinase is 1850 U/L. What is the most appropriate immediate next step in management?