A 52-year-old man with schizophrenia has been stable on haloperidol 10 mg daily for 2 years. Over the past 3 days, he developed fever (39.8°C), severe muscle rigidity, altered mental status, and autonomic instability (BP 160/95, HR 118). His creatine kinase is 3200 U/L and serum creatinine has risen from 0.9 to 1.8 mg/dL. Urinalysis shows myoglobin. What is the most appropriate immediate management?