Byetta Cancer Side Effects May Require Strict Warnings: FDA Officials

Federal drug safety reviewers say that the side effects of Byetta, a diabetes drug, may share thyroid cancer concerns of similar medications, which may result in black-box warning for a new long-acting version of the drug. 

In a report released earlier this month (pdf), FDA officials said animal testing revealing thyroid cancer links with Novo Nordisk’s Victoza, a long-acting diabetes treatment medication, could affect all similar drugs, including Amylin Pharmaceutical’s proposed once-weekly Byetta shot, Bydureon, also known as Byetta LAR. Therefore, strict label warnings may be necessary about the potential Byetta cancer risk to alert users to the possibility of thyroid tumors.

Byetta (exenatide) and Victoza (liraglutide) belong to the same class of drugs, known as GLP-1 analogs. The FDA report expresses concerns that all extended-release diabetes drugs belonging to that family may be linked to thyroid tumors based on tests conducted on rats and monkeys. Victoza was approved in January, but carries the black box warning on potential thyroid cancer. Amylin’s bid for approval of Bydureon was rejected by FDA last month, with the agency requesting more information before it could release the drug on the market.

In April of last year, when concerns regarding Byetta thyroid cancer side effects came up, Amylin pointed out that Victoza and Byetta are different molecules, and indicated that there was no evidence of any link between Byetta and thyroid cancer. However, a statement from company officials following the FDA report concedes that cancer concerns, while not proven, cannot be ruled out as a side effect of Byetta.

Byetta is a type 2 diabetes drug that is manufactured and distributed jointly by Amylin and Eli Lilly & Co. The drug is used to control blood sugar levels and is part of a class of medications known as incretin mimetics, which imitate natural hormones that lower blood glucose levels.

FDA drug safety reviewers have already expressed concerns that Byetta may be linked to kidney failure and a possible increased risk of pancreatitis. In November, the FDA issued a warning indicating that they have received at least 78 post-marketing reports involving Byetta kidney problems, with 62 of those reports involving users experiencing kidney failure. The alert followed FDA warnings issued in October 2007 and August 2008 of reports involving cases of pancreatitis with Byetta, including severe reports of hemorrhagic pancreatitis and necrotizing pancreatitis, which can be fatal.

Amylin and Eli Lilly also currently face a number of Byetta lawsuits involving allegations that the drug makers failed to adequately warn about the risk of pancreatitis and kidney failure.