A 72-year-old man with long-standing hypertension and CKD (eGFR 38 mL/min/1.73 m²) remains hypertensive (160/95 mmHg) despite maximally tolerated doses of ACE inhibitor, calcium channel blocker and thiazide-like diuretic. His adherence is good, and secondary causes have been excluded. Which is the most appropriate next pharmacological step?