Objectives Aliskiren is a novel, orally active renin inhibitor. Its antihypertensive efficacy and safety, alone and in combination with hydrochlorothiazide (HCTZ), were investigated in an 8-week, double-blind, placebo-controlled trial in hypertensive patients. The effects of these treatments on plasma renin activity (PRA) were also assessed.

Methods A total of 2776 patients aged≥18 years with mean sitting diastolic blood pressure (MSDBP) 95–109mmHg were randomized to receive once-daily treatment with aliskiren (75, 150 or 300 mg), HCTZ (6.25, 12.5 or 25 mg), the combination of aliskiren and HCTZ, or placebo, in a factorial design. The primary endpoint was the change in MSDBP from baseline to week 8. PRA was assessed at these timepoints at selected study centers.

Results Aliskiren monotherapy was superior to placebo (P <0.001；overall Dunnett’s test) in reducing MSDBP and mean sitting systolic blood pressure (MSSBP). Combination treatment was superior to both component monotherapies in reducing BP (maximumMSSBP/MSDBP reduction of 21.2/14.3mmHg from baseline with aliskiren/HCTZ 300/25 mg), and resulted in more responders (patients with MSDBP < 90mmHg and/or ≥10mmHg reduction) and better control rates (patients achieving MSSBP/MSDBP<140/90mmHg) than either monotherapy. Aliskiren monotherapy reduced PRA by up to 65% from baseline. Although HCTZ monotherapy increased PRA by up to 72%, PRA decreased in all of the combination therapy groups. All active treatments were well tolerated.

Conclusions Aliskiren monotherapy demonstrated significant BP lowering, and its effect was considerably greater when combined with HCTZ. Renin inhibition with aliskiren neutralized the compensatory rise in PRA induced by HCTZ.

Renin inhibition with aliskiren provides additive antihypertensive  efficacy when used in combination with hydrochlorothiazide