How well does the evidence on pioglitazone back up researchers' claims for a reduction in macrovascular events?

Introduction

Last month, members of the steering committee of the prospective pioglitazone clinical trial in macrovascular events (Proactive) presented the results at the European Association for the Study of Diabetes meeting in Athens.1 The audience, which overflowed from the meeting room, heard John Dormandy, chair of the steering committee, conclude that the trial had shown that pioglitazone, “Reduces the composite of all cause mortality, non-fatal myocardial infarction, and stroke.” He commented: “We have now shown for the first time that oral glucose lowering medication can prevent macrovascular events.” The audience seemed excited by these results and a consensus emerged that the results would change practice. The presentation was certainly positive and upbeat (as readers may judge for themselves from the webcast made available with the support of the study sponsors, Eli Lilly and Takeda1). Unfortunately, these conclusions are not based on robust standards for the interpretation of evidence from clinical trials.

The trial

The trial studied over 5000 patients with inadequately controlled type 2 diabetes randomised to receive pioglitazone or matched placebo. Participants had raised cardiovascular risk, and most were receiving treatment for cardiovascular disease. The minimum planned exposure to study treatment was 2.5 years. The trial seems to have been carried out to a high standard, as we should expect from an industry sponsored trial that was conducted largely to answer safety concerns among regulatory agencies. So why are the conclusions unsafe?

The answer lies with the …