Teva Pharmaceuticals Industries, maker of the world's best-selling multiple sclerosis drug Copaxone, has asked the US regulator not to approve Biogen Idec's investigational pill for the disease, BG-12, citing safety concerns.

The Israeli drugmaker has filed a citizen’s petition requesting that the US Food and Drug Administration refrain from approving any new drug for the treatment of MS until the agency has considered the recommendations of the appropriate expert advisory committee. In particular it has Biogen's BG-12 (dimethyl fumarate) in its sights and no meeting of the FDA's Peripheral and Central Nervous System Advisory Committee is planned for the drug, which is due to be marketed as Panoplin.

Teva's petition makes particular reference to safety concerns that have been linked to two other MS drugs, specifically the problem of progressive multifocal leukoencephalopathy seen with Biogen/Elan's Tysabri (nataluzimab) and Novartis' oral treatment Gilenya (fingolimod), which had its label changed a year after approval to reflect the potential for cardiac problems. Teva adds that although Gilenya was referred to an advisory committee prior to approval, "this just underscores the complex and unpredictable safety concerns associated with MS drugs".

The company then tears into Biogen, saying that the US biotech major "recently posted some troubling information about the safety and effectiveness of Panoplin on a publicly accessible website". Teva adds that in addition to "constituting unlawful, pre-approval promotion of an unapproved drug product, the website contained animal toxicology data" suggesting that the drug may carry potential risks for renal adverse events.

Kidney changes were observed in mice, rats, dogs and monkeys, but Teva says "the fact that renal toxicity was seen across all species studied is concerning and suggests that there is a substantial probability the risk is applicable to humans as well".

Biogen does not seem to be overly-concerned by the claims, noting that BG-12’s safety issues, which include flushing, diarrhoea, and nausea, are  manageable, noting that human studies show there are no known risks of cancer, serious infections or other major events, The renal side effects were similar in clinical trials whether a patient was on BG-12 or placebo.

In October, the FDA told Biogen it needed another three months to review the drug so a final decision is not expected until March. Most observers expect approval for BG-12, which will compete with Teva's injectable MS blockbuster Copaxone (glatiramer acetate).