A 55-year-old female developed ESRD due to poorly controlled diabetes. She underwent dialysis 2-3 times a week. She was advised for kidney transplant which she received from cadaveric donor. She was put on immunosuppressive therapy with azathioprine, cyclosporine, methylprednisolone and anti-thymocyte globulin. Two weeks following the surgery, the patient was discharged on medications. 2 weeks later she presented to emergency with complaints of decreased urine output. On examination, her BP was noted to be 160/95 mm hg. The region of the graft is enlarged and is tender to touch. Lab investigations revealed serum creatinine of 4 mg/dl. Her differential diagnosis includes transplant rejection and drug toxicity. Which drug could be held responsible for the above clinical scenario?