A 52-year-old man with a 10-year history of type 2 diabetes mellitus presents to the nephrology clinic. His blood pressure is 148/92 mmHg despite amlodipine 5 mg daily. Serum creatinine is 2.8 mg/dL (baseline 1.2 mg/dL 2 years ago), eGFR is 28 mL/min/1.73m², and urine albumin-to-creatinine ratio (UACR) is 450 mg/g. Urinalysis shows 2+ proteinuria. Renal ultrasound shows normal-sized kidneys with increased echogenicity. Which of the following is the most appropriate next step in management to slow progression of his chronic kidney disease?