Onyx Pharmaceuticals announced today that it is delaying for at least six months its application to market carfilzomib ^[1], a new treat­ment for multiple myeloma, in the United States.

Prior to today’s announcement, Onyx had expected to submit car­filz­o­mib’s new drug application to the U.S. Food and Drug Administration (FDA) by the end of this year.

Now the com­pany says its application will be submitted “as early as mid-year 2011.”

In its announcement today, Onyx explained that the delay in car­filz­o­mib’s U.S. marketing timeline is due to an FDA request for addi­tional in­­for­ma­tion about manu­fac­tur­ing plans for the drug.

This request, in turn, was sparked by tests that revealed “variations” in the car­filz­o­mib being produced using new manu­fac­tur­ing processes Onyx is implementing.

The com­pany is emphasizing that the new marketing timeline for car­filz­o­mib is not due to any change in the expected efficacy or safety of the drug. Onyx says that “Phase 3 trials [of car­filz­o­mib] are on schedule and actively enrolling patients, and this change is not expected to impact any of the car­filz­o­mib trials.”

Carfilzomib works similarly to the existing multiple myeloma treat­ment Velcade ^[2] (bor­tez­o­mib) by preventing the breakdown of protein in cancer cells, triggering their death.

Along with pomalidomide ^[3] – a chemical relative of multiple myeloma drugs Revlimid ^[4] (lena­lido­mide) and thalidomide ^[5] (Thalomid) – car­filz­o­mib is considered one of the most promising myeloma treat­ments that could be approved by the FDA in the next few years.

Based on the new application timeline for car­filz­o­mib and assuming no further delays in the application and approval process, the drug should be available for sale in the United States in the first half of 2012.  Onyx has not yet announced a timeline for the marketing of car­filz­o­mib elsewhere in the world.

For further details on today’s announcement by Onyx, please see the com­pany’s press release ^[6]. For several articles summarizing recent car­filz­o­mib trial results, see The Myeloma Beacon’s coverage ^[7] of the ASCO 2010 annual meeting.