A 32-year-old woman with systemic lupus erythematosus (SLE) presents to the emergency department with acute onset fever (39.2°C), severe abdominal pain, and bloody diarrhea 3 days after starting sulfasalazine for joint symptoms. Physical examination reveals diffuse abdominal tenderness and hyperactive bowel sounds. Laboratory investigations show: WBC 8,200/μL, hemoglobin 11.2 g/dL, platelets 180,000/μL, and stool culture is negative for pathogens. Colonoscopy reveals mucosal ulceration and inflammation. The patient denies recent antibiotic use or sick contacts. Which type of adverse drug reaction best classifies this presentation?