A 58-year-old man with a 10-year history of type 2 diabetes mellitus presents to the nephrology clinic. His serum creatinine is 2.8 mg/dL, eGFR is 22 mL/min/1.73m², and urinary albumin-to-creatinine ratio (UACR) is 450 mg/g. He is currently on metformin, amlodipine, and lisinopril. His blood pressure is 138/88 mmHg. What is the most appropriate next step in management?