S-amlodipine plus chlorthalidone vs. S-amlodipine plus telmisartan in hypertensive patients unresponsive to amlodipine monotherapy: study protocol for a randomized controlled trial.

BACKGROUND: The efficacy of a combination of a calcium channel blocker (CCB) plus chlorthalidone (diuretic) versus a CCB plus an angiotensin receptor blocker (ARB) in patients not responding to CCB monotherapy has not been evaluated previously. We plan to compare the efficacy and safety of S-amlodipine (CCB) plus chlorthalidone versus S-amlodipine plus telmisartan (ARB) combinations among hypertension patients unresponsive to amlodipine monotherapy.

METHODS/DESIGN: This study is a prospective, randomized, double-blind, multicenter, parallel, non-inferiority phase 4 study. Hypertension patients who have been treated with amlodipine (5 mg) or S-amlodipine (2.5 mg) monotherapy for ≥2 weeks and whose mean diastolic blood pressure (DBP) is greater than 90 mmHg will be randomized to either S-amlodipine (2.5 mg) plus chlorthalidone (25 mg) or S-amlodipine (2.5 mg) plus telmisartan (40 mg) therapy. The primary efficacy endpoint is mean sitting DBP change after 12 weeks of treatment. The study objective is to prove the non-inferiority of the former combination (test drug) as compared to the latter one (control) with a non-inferiority margin of 3 mmHg in mean DBP change. The secondary endpoints are 6-week DBP change, 6- and 12-week sitting systolic BP (SBP) change, and the attainment of the target BP (SBP < 140 mmHg or DBP < 90 mmHg). Urine albumin, albumin/creatinine ratio (ACR), pulse wave velocity, central BP, 24-h ambulatory BP monitoring, and body fluid composition analysis will be performed at each hospital's discretion. The sample size was estimated as 170 in total with 1:1 randomization.

DISCUSSION: This is the first study comparing the efficacy of a CCB plus chlorthalidone versus a CCB plus an ARB in patients who are not responding to CCB single therapy. The study result will help clinicians to choose between chlorthalidone and telmisartan in CCB-unresponsive patients.

TRIAL REGISTRATION: ClinicalTrials.gov , NCT03226340. Registered on 2 December 2015.