A 68-year-old man with long-standing type 2 diabetes and hypertension has an eGFR of 60 mL/min/1.73 m² and a urinary albumin-creatinine ratio (ACR) of 12 mg/mmol on two occasions. His blood pressure is 138/82 mmHg on amlodipine alone. What is the most appropriate next step to slow progression of kidney disease?