Magnitude of blood pressure reduction in the placebo arms of modern hypertension trials: Implications for trials of renal denervation

Early phase studies of novel interventions for hypertension, such as renal sympathetic denervation, are sometimes single-armed (uncontrolled). We explored the wisdom of this by quantifying the blood pressure fall in the placebo arms of contemporary trials of hypertension. We searched Medline up to June 2014 and identified blinded, randomized trials of hypertension therapy in which the control arm received placebo medication or a sham (placebo) procedure. For nonresistant hypertension, we have identified all such trials of drugs licensed by the US Food and Drug Administration since 2000 (5 drugs). This US Food and Drug Administration-related restriction was not applied to resistant hypertension trials. This produced 7451 patients, who were allocated to a blinded control from 52 trials of nonresistant hypertension and 694 patients from 8 trials of resistant hypertension (3 drugs and 2 interventions). Systolic blood pressure fell by 5.92 mm Hg (95% confidence interval, 5.14-6.71; P<0.0001) in the nonresistant cohort and by 8.76 mm Hg (95% confidence interval, 4.83-12.70; P<0.0001) in the resistant cohort. Using metaregression, the falls were larger in trials that did not use ambulatory blood pressure monitoring as an inclusion criterion (z=2.84; P=0.0045), in those with higher baseline blood pressures (z=-0.3; P=0.0001), and in those where the patients were prescribed a continuous background of antihypertensives (z=-2.72; P=0.0065). The nontrivial magnitude of these apparent blood pressure reductions with perfectly ineffective intervention (placebo) illustrates that efficacy explorations of novel therapies for hypertension, once safety is established, should be performed with a randomized, appropriately controlled, and blinded design.