A 44-year-old woman, who underwent liver transplantation for autoimmune hepatitis three years ago, has been maintained on tacrolimus monotherapy as immunosuppressive therapy for 2.5 years. Her serum creatinine has slowly risen over the 8 months from 1.4 mg/dl to 2.1 mg/dl. Spot urinalysis shows 2 + proteinuria.

Which of the following is the most appropriate strategy to preserve her renal function while decreasing the risk of developing rejection?