A 65-year-old man is evaluated during a follow-up visit for stage G3b/A3 chronic kidney disease due to diabetic nephropathy. He reports doing well with good baseline exercise tolerance and no shortness of breath. Medical history is also significant for type 2 diabetes mellitus and hypertension. Medications are basal bolus insulin and lisinopril, 20 mg/d.

On physical examination, temperature is normal, blood pressure is 145/75 mm Hg, pulse rate is 82/min, and respiration rate is 16/min. BMI is 28. There is no jugular venous distention. The lungs are clear.

Laboratory studies:

Bicarbonate

Normal

Creatinine

1.9 mg/dL (168 µmol/L)

Potassium

4.0 mEq/L (4.0 mmol/L)

Estimated glomerular filtration rate

42 mL/min/1.73 m2

Urine protein-creatinine ratio

3900 mg/g

Kidney ultrasound shows mildly echogenic kidneys that are of normal size with no obstruction.

Which of the following is the most appropriate treatment?