A 62-year-old woman with chronic kidney disease stage 3b has a serum creatinine of 1.8 mg/dL and estimated GFR of 35 mL/min/1.73 m². Her urine albumin to creatinine ratio is 400 mg/g. She has well-controlled diabetes and hypertension on lisinopril and amlodipine. According to current kidney disease recommendations, which additional medication is most appropriate to slow progression of kidney disease?