correspondence questions PROactive conclusions
January 11, 2006
London, UK - Correspondence in the January 7, 2006 issue of the Lancet raises questions about the conclusions of the recently published Prospective Pioglitazone Clinical Trial in Macrovascular Events (PROactive) trial.
PROactive compared treatment with pioglitazone (Actos, Takeda Pharmaceutical Company/Eli Lilly) vs placebo in patients with type 2 diabetes at high risk for macrovascular events. The main results, published in the October 8, 2005 issue of the Lancet, showed a nonsignificant 10% reduction in the study's primary end point of all macrovascular events vs placebo but found a significant 16% reduction in the secondary composite end point of death, MI, and stroke with pioglitazone treatment .
The authors' conclusion that pioglitazone "reduces the composite of all-cause mortality, nonfatal myocardial infarction, and stroke in patients with type 2 diabetes who have a high risk of macrovascular events" draws fire from Lancet readers in this week's issue.
Concerns about interpretation
Several letters took issue with the fact that this conclusion was based largely on results from the secondary composite end point. For example, Dr Pierre-Jean Guillausseau (University Paris, France) points out, "Although the study is globally negative, a new 'main secondary end point' appeared?ie, a new composite not described in the study protocol published in 2004. The conclusions of the study are based solely on this composite. "
The results should be adjusted for mean differences in hemoglobin A1c (HbA1c) and blood pressure, and there remains a major concern about the increased incidence of heart failure seen with pioglitazone, Guillausseau adds. "Thus several questions remain, and the role of glitazones in type 2 diabetes mellitus is not yet fully defined."
In a separate letter, Drs Peter Gaede, Hans-Henrik Parving, and Oluf Pedersen (Steno Diabetes Center, Copenhagen, Denmark) point out that patients receiving pioglitazone had a greater decrease in HbA1c than those on placebo, although LDL increased with treatment. However, blood pressure was also lower in treated patients, by about 3 mm Hg .
"An accurate prediction of the relative risk reduction of a 3-mm-Hg systolic gradient seen in PROactive indicates that this is more than sufficient to explain the whole potential cardiovascular benefit of pioglitazone," they write. "Furthermore, it should be stressed that this prediction is conservative, since diabetic patients are particularly blood-pressure sensitive."
"Hypothesis generating," not "groundbreaking proof"
Drs John S Yudkin (University College London, UK) and Nick Freemantle (University of Birmingham, UK) are blunter . In concentrating on the "main secondary end point," they write, the PROactive authors "ignore the statistically neutral primary outcome. One assumes that, had the 10% reduction in primary-end-point events been significant, Dormandy and colleagues would have felt no need to emphasize the analysis of the main secondary end point," an end point that should be considered "hypothesis-generating" rather than "groundbreaking proof."
An appropriate conclusion from PROactive, Yudkin and Freemantle assert, "is that glitazones reduce cardiovascular event rates with a point estimate of around 10% to 15%, but with a confidence interval including zero?a result in line with the equally uncertain reduction in macrovascular events seen in the United Kingdom Prospective Diabetes Study (UKPDS). Judging from the way in which the results were presented at the European Association for the Study of Diabetes in Athens in September 2005 and from the website (http://www.proactive-results.com), there is a risk that the marketing division of Takeda and Eli Lilly will use these questionable results mercilessly in their promotional material."
Freemantle also voiced his objection to the PROactive conclusions in a letter previously published by the BMJ .
Finally, Drs RR Holman, R Retnakaran, A Farmer, and R Stevens (Churchill Hospital, Oxford UK) write that they carried out an analysis using the UKPDS Outcomes Model to assess the expected outcomes given the risk-factor changes reported . They point out that the nonsignificant 10% relative risk reduction seen with pioglitazone treatment on the primary end point was less than the 20% or more on which the power calculation for the study was based.
"Our analysis supports the explanation that any macrovascular benefits seen reflect the modest improvements obtained in established risk factors, with little evidence that changes seen previously in novel risk factors with pioglitazone have any substantive effect," they write. "More worryingly, the estimated macrovascular benefits are offset by an increased risk of heart failure and concerns about increased peripheral revascularization rates."
The authors respond
In a response undersigned by the principal investigator of the PROactive study, Dr John Dormandy (St Georges Hospital, London, UK), the PROactive investigators defend their interpretation of the main secondary end point . "As described in the PROactive report, this end point was prespecified in the statistical analysis plan and submitted to the Food and Drug Administration before unblinding," they write. "It showed a 16% relative risk reduction with pioglitazone (p=0.027).
"We agree that in isolation this finding would not allow any definite conclusion to be drawn," Dormandy et al add. "However, the primary composite end point, which also included silent myocardial infarction, acute coronary syndrome, major leg amputation, and coronary and leg revascularization, also showed a reduction with pioglitazone?10% relative risk reduction (p=0.095)."
To the comment made by Yudkin and Freemantle about how they would have felt no need to present the main secondary-end-point analysis if the primary end point had been significantly positive, they respond, "On the contrary, it is the effect on mortality, myocardial infarction, and strokes that would be of most interest to patients and the regulatory authorities."
As for the increase in heart failure, they point out that the heart-failure events in this study were unadjudicated and the diagnoses made by the investigators, "who might have been sometimes misled by the known increase in edema with pioglitazone," Dormandy et al write.
"We are surprised by the comparison in the Comment [the editorial accompanying the PROactive publication by Dr Hannele Yki-J¿rvinen (University of Helsinki, Finland) (8)] of first events for end points avoided, on the positive side, vs all episodes of heart failure, on the negative side," they add. "Nevertheless, the executive committee is further exploring the issue of heart failure by setting up an independent commission of experts to review, in a blinded way, all source material for patients reported to have had fatal or nonfatal heart failure at any time during the trial."
Disclosure information is provided for correspondents and PROactive authors in the Lancet publication.
Dormandy JA, Charbonnel B, Eckland DJA, et al on behalf of the PROactive investigators. Secondary prevention of macrovascular events in patients with type 2 diabetes in the PROactive Study (Prospective Pioglitazone Clinical Trial in Macrovascular Events): a randomized controlled trial. Lancet 2005; 366:1279-1289. Guillausseau PJ. PROactive study. Lancet¿2006;¿367:23. Gaede P, Parving HH, and Pedersen O. PROactive study. Lancet¿2006;¿367:23-24. Yudkin JS, Freemantle N. PROactive study. Lancet¿2006;¿367:24-25. Freemantle N. How well does the evidence on pioglitazone back up researchers' claims for a reduction in macrovascular events? BMJ 2005; 331:836-838. Holman RR, Retnakaran R, Farmer A, and Stevens R. PROactive study. Lancet¿2006;¿367:25-26. Dormandy J. PROactive study?Authors' reply. Lancet¿2006;¿367:26-27. Yki-J¿rvinen H. The PROactive study: some answers, many questions. Lancet 2005; 366:1241-1242.
This is a part of article correspondence questions PROactive conclusions Taken from "Actos Pioglitazone" Information Blog