Is ezetimibe/simvastatin no better than simvastatin alone? Lessons learned and clinical implications
The Ezetimibe and Simvastatin in Hypercholesterolemia Enhances Atherosclerosis Regression (ENHANCE) trial1 was probably the most widely publicized clinical study of the past decade. How did a 720-patient imaging trial with a neutral result in patients with severe hypercholesterolemia rise to a level warranting massive media attention, a congressional investigation, and a recommendation to curtail the use of a drug widely used to reduce levels of low-density-lipoprotein cholesterol (LDL-C)?
The reaction to the ENHANCE trial reveals more about the political climate and the relationship between the pharmaceutical industry and the American public than it does about the effects of ezetimibe (available combined with simvastatin as Vytorin and by itself as Zetia) on the progression of atherosclerosis.
SOME SELF-DISCLOSURE
Before I discuss the clinical implications of the ENHANCE trial, I must describe both my financial conflicts and intellectual biases. I am a paid consultant, speaker, and researcher on behalf of Merck/Schering-Plough, the sponsor of the ENHANCE trial. I was a principal investigator in the first phase II trial of ezetimibe and have conducted more than 10 clinical trials of either ezetimibe or ezetimibe/simvastatin. I also have been a strong advocate for imaging trials to assist in the clinical development of novel therapeutic agents and to support regulatory approval.
Therefore, I believe that the thickness of the intima and media layers of the carotid arteries is a useful surrogate to evaluate the potential antiatherosclerotic effects of drugs (more on this topic below). Also, I believe that the LDL-C-lowering hypothesis has been proven: ie, that all drugs that lower LDL-C safely, without off-target adverse effects, should reduce cardiovascular events. I support the goal levels of LDL-C and non-high-density-lipoprotein cholesterol set by the National Cholesterol Education Program’s third Adult Treatment Panel (ATP III) guidelines,2,3 which specify LDL-C targets rather than the use of specific drugs. In spite of these conflicts and potential biases, I believe I have always served the best interests of patient care.
HISTORY OF THE ENHANCE TRIAL
The end point defined as the mean of six measurements
The primary end point was the change in the thickness of the intima and media layers of the carotid arteries over a 2-year period, measured by ultrasonography. A composite measure was used: the mean of the thicknesses in the far walls of the right and left common carotid arteries, the right and left carotid bulbs, and the right and left internal carotid arteries. Secondary end points included the change in the mean maximal carotid artery intima-media thickness (ie, the thickest of the six baseline measurements), the proportion of participants who developed new carotid artery plaque (defined arbitrarily as an intima-media thickness > 1.3 mm), and changes in the mean of the intima-media thickness of the six carotid sites plus the common femoral arteries.
The last participant completed the trial in April 2006. Reading of the almost 30,000 scans was not started until the last participant was finished, so that all scans for each participant could be read in a blinded, randomized order by five separate readers. A significant proportion of the images that the protocol called for could not be obtained or analyzed, particularly in the internal carotid artery and the carotid bulb, which are often difficult to visualize. As a result, 17% of the internal carotid or carotid bulb measurements were discarded.
To change the end point post hoc, or not to change the end point?
The sponsor of the trial was concerned about the missing data points and convened a special advisory board to review the blinded data. This group suggested a solution: changing the primary end point from the six-site composite value to the mean value in just the common carotid arteries. They based this suggestion on the greater success rate in measuring the common carotids (97%) than in measuring all six sites (88%), as well as on recent trials that indicated that the common carotid artery measurement correlates better with clinical outcomes (because the internal carotid and the bulb measurements vary more). On November 26, 2007, Merck/Schering-Plough announced the primary end point would be changed to the mean change in the common carotid arteries.
However, during a separate meeting on November 30, 2007, some members of the Merck/Schering-Plough advisory board objected to the change. On December 11, 2007, the company announced that the original primary end point would not be changed.
