US consumer watchdog Public Citizen has petitioned the Food and Drug Administration to pull Roche’s obesity drug Xenical (orlistat) from the market, after its review of available clinical data linked the agent to the development of precancerous colon lesions in rats.

According to the group, the FDA’s own review of Xenical back in 1997 highlighted colonic cell proliferation as a concern, and the drug was initially turned down for approval on clinical trials that found a four-to-seven-fold increased risk of getting breast cancer.

In addition, Public Citizen said recent data from two clinical trials showed just a 2.8% difference in weight loss after four years in patients taking the drug and those given a placebo, casting doubt on the product’s efficacy as well as its safety profile. “The FDA should not allow a drug…to remain on the market for the long-term treatment of a non-lethal condition when it combines so little efficacy coupled with a still unresolved potential to cause breast and colon cancer,” the group’s petition states.

And given the heightened safety concerns over use of the agent, it has also requested that the FDA rejects GlaxoSmithKline’s application to sell an over-the-counter version of Xenical, after an approvable letter was issued to the drugmaker last week. GSK owns non-prescription rights to the drug in the US, and will be able to market its OTC version once conditions set out in the letter are met.

With an estimated two-thirds of Americans either overweight or obese, OTC orlistat, which will be sold as Alli (pronounced AL-eye) in the USA, has the potential to become a major non-prescription drug brand with blockbuster sales potential. GSK has said it plans to make Alli available at a cost of around $12 to $15 a week, and expects could be used by 5 to 6 million consumers, which could bring in sales of $1.5 billion or more.

According to Dr Sidney Wolfe, director of Public Citizen’s Health Research Group, “the failure to ban the prescription version of this drug or, worse, to make it much more widely available by allowing OTC sales, is a decision that is likely to increase cancer incidence.”

But a spokesman for Roche told PharmaTimes World News that the company is confident in the safety of Xenical as a weight-loss therapy. “Xenical is the most extensively studied pharmacological weight treatment today. Its safety profile is supported by 100 clinical studies in 30 different countries with over 30,000 patients participating,” he said. “Consumers should continue to feel safe taking the product.”