The US Food and Drug Administration has asked the makers of two antidiabetes drugs—rosiglitazone (marketed as Avandia), made by GlaxoSmithKline, and pioglitazone (Actos), made by Takeda—to place “black box” warnings, the most serious kind, on their labels.

The new labels warn of an increased risk of congestive heart failure, because rosiglitazone and related drugs can cause fluid retention. Andrew von Eschenbach, the FDA's commissioner, announced the warning at a hearing of the US House of Representatives' Committee on Oversight and Government Reform last week to examine the FDA's role in evaluating the safety of rosiglitazone.

The new labels do not address the question of whether these drugs pose an increased risk of heart attacks and strokes.

The cardiovascular risk was raised last month by an article and accompanying editorial in the New England Journal of Medicine (doi: 10.1056/NEJMoa072761). Steven Nissen and Kathy Wolski of the Cleveland Clinic did a meta-analysis of publicly available data and concluded that rosiglitazone was associated with a significant 43% increase in the risk of heart attack (BMJ 2007;334:1073, 26 May, doi: 10.1136/bmj.39224.364630.DB).

On 5 June the New England Journal of Medicine published three online editorials related to “continued uncertainty” about rosiglitazone, together with an interim analysis of the cardiovascular outcomes …