GlaxoSmithKline shares have taken a fresh hit this morning on the news that Avandia’s share of the market for newly prescribed oral anti-diabetics has sunk without trace after the study published last week which linked the drug to cardiovascular events.

According to early prescription data published by the market intelligence group Impact RX, the share of the market enjoyed by Avandia (rosiglitazone) for newly prescribed OADs fell to approximately zero from around 10% in the two days after the aforementioned article appeared in the New England Journal of Medicine on May 21. The study published in the latter, and criticised by GSK, concluded that the drug increased the risk of heart attack by 43% and cardiac-related death by 64%.

The Impact Rx data was cited in a note issued by Deutsche Bank analysts who said that new and switch prescription data from 1,900 US primary care physicians showed Avandia's average share of the newly written OAD prescription market on May 21, 22 and 23 was 10%, 8% and 6% respectively, which suggests that its share dropped to almost zero on May 22 and 23. "This reaction is far worse than we had anticipated and suggests that there could be as much as 22% downside risk to GSK's near term earnings,” suggesting that there is still further downside to the firm’s share price," Deutsche Bank said.

The data also notes that the rate of patients switching from one drug to another was three times the usual level, with Takeda Pharmaceutical Co’s Actos (pioglitazone) increasing its share of the new prescription market from 10% to 22%.

RECORD study affected from drop-outs

Alas for GSK, the furore around the NEJM study shows no sign of abating and it is feared that the company’s major ongoing RECORD study may be affected by patients dropping out of the trial. The firm’s chief medical officer, Ronald Krall, told the New York Times commented that independent research committees overseeing the RECORD study "are concerned about the ability of the study to continue [and are] considering what to do to prevent people from dropping out of the trial”.

The 4,450-patient study is scheduled to continue until the end of 2008, and GSK has been hoping that a successful outcome from the trial will serve to dispel the widespread concerns around Avandia.