A 32-year-old woman on sertraline 100 mg daily for depression is started on tramadol 50 mg TDS for chronic back pain by an orthopaedic surgeon unaware of her psychiatric medication. Within 48 hours, she develops tremor, hyperreflexia, clonus, agitation, and a core temperature of 38.5°C. She is brought to the emergency department. What is the most appropriate immediate next step in management?