The US Food and Drug Administration has once again rejected Teva Pharmaceutical Industries’ request to stop approval of any generic versions of the Israeli company’s multiple sclerosis blockbuster Copaxone.

Last year, Teva asked the FDA to block copycat versions of Copaxone (glatiramer acetate) after the agency had accepted for review Abbreviated New Drug Applications from Momenta Pharmaceuticals and Novartis unit Sandoz, as well as Mylan. The Petah Tikva-headquartered firm’s argument was that Copaxone is “a complex mixture of the acetate salts of synthetic polypeptides” and due to “the variability of the composition of the polymers”, it believes that “replicating this formulation would be extremely difficult”.

However the FDA rejected that claim and has now turned down a second Citizen’s Petition for the same reason, namely that it would be “premature and inappropriate” to grant Teva's requests. The agency speaks of its “broad discretion" in determining whether the submitted information by Momenta/Sandoz and Mylan, or anyone else, is enough to conclude that a generic is the same as the original.

The FDA adds that “a finding of sameness does not, however, necessitate a finding of ‘complete chemical identity’. Thus, the agency may consider other criteria to determine sameness, taking into account the complexity of the active ingredient”.

Despite this latest rejection, the FDA said the information in Teva's letter will help it assess of the types of information required to support generic Copaxone. The world’s biggest generics firm has already sued Momenta/Sandoz and Mylan which means that no generic version can enter the US market until early 2011.

First-quarter sales of Copaxone reached $796 million, an increase of 28%.