The US Food and Drug Administration (FDA) has requested additional information on Teva Pharmaceutical Industries‘ biosimilar version of Amgen‘s chemotherapy drug Neupogen before it decides whether to grant approval.

The application for the drug, called Neutroval, was filed using a traditional approval pathway for a biologic drug. However, the drug is sold as a biosimilar to Neupogen in Europe under the name TevaGrastim.

Biosimilars are close generic versions of complex biologic drugs for which the FDA has yet to release guidance on the approval pathway, despite including provisions for such drugs in the March healthcare overhaul.

Teva’s FDA submission in November included results from five clinical studies of the drug, which received approval in Europe in September 2008.

The delay in the approval process adds to the controversy surrounding the drug, which began after Amgen filed a patent-infringement claim in federal court to block the generic.

A trial date is yet to be set, but Amgen will be widely expected to file for an injunction to block any Teva launch if the FDA eventually approves the drug.