A 40-yeаr-оld mаn with а histоry оf uncontrolled diabetes presents to the clinic for his yearly follow-up. His recent laboratory tests show sodium 132 mEq/L (normal 136–145 mEq/L), creatinine 1.4 mg/dL, GFR 55 mL/min/1.73 m2, and glucose 450 mg/dL. His urinalysis is positive for glucose. He is asymptomatic. Which of the following is high priority and next step in his management?