Q. A 55-year-old man visits the nephrology clinic to have his metabolic acidosis and hyperkalemia evaluated. His medical history is significant for both hypertension and a kidney transplant. He has been taking cyclosporine for the past 2 months. On examination, he is found to have a heart rate of 88/min and a blood pressure of 150/90 mm Hg. No edema is detected. Lab results show his serum potassium level is 7.2 mEq/L, creatinine level 2.5 mg/dL, and the serum bicarbonate level is 10 mEq/L. Which of the following is the most likely underlying cause of these findings?