The war of words between GlaxoSmithKline and critics of the firm’s oral diabetes drug escalated yesterday, as the marketer took additional steps to shore up confidence in Avandia.

In a letter posted on the Web site of The Lancet, GlaxoSmithKline chief medical officer Ronald Krall pointed to three large trials of rosiglitazone that he said demonstrate the cardiovascular safety of the drug—Adopt, Dream and a third unfinished study called Record, which a data safety monitoring board checking for cardiovascular events recently said should continue.

In addition, Krall said GSK did “meta-analyses” similar to the one conducted by Cleveland Clinic cardiologist Steven Nissen. Nissen’s analysis, which sparked the controversy when it appeared in The New England Journal of Medicine last week, estimated that rosiglitazone is associated with a 43% increase in heart attacks. GSK’s in-house meta-analysis found increased risk, too, but the number of adverse events was low.

Nissen criticized the Lancet letter, saying GSK’s interpretation of the Adopt and Dream data differs from the published results and that data subsets referred to in both trials are too small to draw conclusions from.

Meanwhile, GSK US Pharmaceuticals President Christopher Viehbacher, in an interview with The Wall Street Journal, said the Record trial’s interim results were “giving us confidence to say that we stand behind this product.” GSK is bracing for the FDA to call for some labeling changes to Avandia, Viehbacher added, such as elevating the heart-failure warning to a black-box warning.

He was the second high-profile executive from the Anglo firm to publicly back the oral diabetes drug. Last week at a shareholders meeting, CEO JP Garnier said the drug “will be vindicated” once the full data set on Avandia becomes available.