Biogen Idec will have to wait a bit longer to launch its new multiple sclerosis treatment Plegridy after regulators in the USA said they need more time to review the file.

The company says that the  Food and Drug Administration has extended the initial Prescription Drug User Fee Act (PDUFA) date for Plegridy  by three months. This means the agency will give its verdict on marketing approval in the second half of 2014.

Biogen stresses that three months is the "standard extension period" and importantly the FDA has not asked for additional studies. The European filing is progressing on schedule.

Plegridy is a pegylated beta interferon in the same class of MS treatments as Biogen's older MS blockbuster Avonex.. Trials have shown that it significantly reduced relapses, disability progression and brain lesions compared to placebo.

While there is much focus on oral MS drugs, Plegridy is still expected to be a successful product given that it will require less frequent injections and they will be administered subcutaneously. It should therefore be less painful than Avonex (interferon beta-1a) which is given intramuscularly.