GlaxoSmithKline’s type 2 diabetes therapy Avandia will now have to carry a boxed warning that it may "cause or worsen heart failure in certain patients," after US regulators slapped such warnings on the entire class of thiazolidinedione drugs.

"This new boxed warning addresses the Food and Drug Administration’s concerns that, despite the warnings and information already listed on the drug labels, these drugs are still being prescribed to patients without careful monitoring for signs of heart failure," explained Steven Galson, director of the Center for Drug Evaluation and Research.

The agency noted that its review of adverse event reports from patients using thiazolidinedione drugs – including Actos (pioglitazone) includes Avandaryl (rosiglitazone and glimepiride), Avandamet (rosiglitazone and metformin) and Duetact (pioglitazone and glimepride) - found cases of significant weight gain and oedema, warnings signs of heart failure. Furthermore, in some of these reports continuation of therapy had been associated with poor outcomes, including death.

The new boxed warning advises healthcare professionals to look carefully for the signs and symptoms of heart failure in patients, and that these drugs should not be used by people with serious or severe heart failure who have marked limits on their activity and who are comfortable only at rest or who are confined to bed or a chair.

GSK noted that since 2001, US prescribing information for Avandia has included a warning for cardiac failure and other cardiac effects with a recommendation that use of the drug be discontinued in patients if their cardiac status worsened. Increasing the warning comes as no surprise, especially given the prominence that the thiazolidinedione class, and Avandia in particular, has had of late, but Chris Viehbacher, president of US pharmaceuticals at GSK, said on a conference call: "I don't, at this stage, think we're going to see a significant impact on prescribing in terms of dollar value."

Salesforce cut for Avandia?

Meantime, a report in the Telegraph suggests that GSK is thinking about cutting its salesforce for Avandia after prescriptions in the USA plummeted 40%.

The Telegraph reports that the company is reconsidering its marketing strategy for Avandia, and suggests that this could mean trimming its salesforce or moving staff to other projects.

But the claim, made by anonymous sources, was countered by Viehbacher, who insisted that GSK has made “no plans to reduce staff as a result of Avandia issues.” Instead, he said, the company's "immediate focus is to reinforce physician confidence in both the safety and benefits of Avandia."