A 35-year-old woman with uncomplicated urinary tract infection is prescribed ciprofloxacin 500 mg twice daily. She is also taking methotrexate 15 mg weekly for rheumatoid arthritis. On day 2 of fluoroquinolone therapy, she develops nausea, vomiting, and severe abdominal pain. Laboratory investigations show serum creatinine 2.8 mg/dL (baseline 0.9 mg/dL) and elevated liver enzymes. What is the most appropriate next step in management?