Amylin has received a boost from new data which demonstrates that its type 2 diabetes drug Byetta provides a greater reduction in post-meal glucose levels than Merck & Co’s Januvia.

The data comes from the first head-to-head trial directly comparing the therapeutic mechanisms of action of Byetta (exenatide), a glucagon-like peptide-1 agonist partnered with Eli Lilly, and Merck & Co’s dipeptidyl peptidase-4 (DPP-4) inhibitor Januvia (sitagliptin). Presented at the European Association for the Study of Diabetes. Meeting in Rome, the four-week study evaluated 61 patients who were randomly assigned either twice-daily injections of Byetta or once-daily oral Januvia for two weeks, then switched to the alternate therapy for the remaining two weeks.

The data showed that patients who took Byetta for the first two weeks had glucose levels of 133mg per decilitre two hours after a meal, compared with 208mg/dl for those on the DPP-4 inhibitor. As patients were switched from Januvia to the GLP-1 agonist to Byetta, the post-meal glucose was further improved (-76 mg/dl), and when they switched the other way, it worsened (+73 mg/dl).

Ralph DeFronzo of the University of Texas Health Science Center in San Antonio and an investigator on the study said there has been “some confusion in the marketplace about the therapeutic differences between Byetta and Januvia” and the study showed “a clear difference in the MOAs and resultant short-term clinical effects between these two agents”. He added that Byetta works directly on the GLP-1 receptor, whereas Januvia indirectly affects GLP-1 levels and patients on the Amylin drug experienced “significantly lower post-meal glucose levels, improved measures of beta cell function and decreased food intake”.

The data is a boost for Amylin which has seen its shares slide since the details of six deaths among patients with pancreatitis who took Byetta were announced a fortnight ago. However the stock fell again last night, down 6.3% to $18.88 after a report from Lazard Capital Markets revealed that new prescriptions for the drug decreased 2.3% in the first nine weeks of the quarter compared with the like, year-earlier period, while Januvia rose 8.9%.

In a research note, Matthew Osborne at Lazard wrote that "we continue to believe strong demand for Januvia, and not pancreatitis, will pressure Byetta growth, pushing Byetta more towards third- or fourth-line treatment options." Amylin is hoping that this latest data will provide a push to sales but other observers say the study was too short and limited ie using two hours after a meal as a measure for glucose levels.