A 28-year-old Indian woman presents with a 5-day history of fever, malaise, and painful skin lesions. She had started carbamazepine 3 weeks ago for newly diagnosed epilepsy. On examination, she has dusky atypical target lesions on the trunk and extremities, and the structure marked **B** in the diagram shows hemorrhagic crusts with severe pain. She also has conjunctivitis and a positive Nikolsky sign. Her HLA-B*1502 status was not checked before initiating carbamazepine. What is the MOST appropriate IMMEDIATE management step?