The US Food and Drug Administration (FDA) this week began adding four-letter meaningless suffixes at the end of newly approved biologics' nonproprietary names, signaling a shift in policy from only adding the suffixes to biosimilars' nonproprietary names since 2015.

The first additions of the meaningless suffixes came for Thursday's approval of Roche's Hemlibra (emicizumab-kxwh), one of the first new medicines in nearly two decades to treat people with hemophilia A, and Wednesday's approval of Ultragenyx Pharmaceutical's Mepsevii (vestronidase alfa-vjbk) to treat pediatric and adult patients with a rare inherited condition called mucopolysaccharidosis type VII (MPS VII), also known as Sly syndrome.

The newly added suffixes were not preceded by an announcement from FDA, though the shift was not entirely unexpected.

Back in January, FDA finalized guidance on how biosimilars and their biologic reference products' names should include this four-letter, FDA-designated meaningless suffix attached at the end of the nonproprietary name.

But until this week, only new biosimilars had the suffixes attached to their names. The agency did not respond to a request for comment on why new biologics' nonproprietary names included the suffixes this week.

In addition, some biosimilars have yet to be assigned meaningless suffixes. For example, the first biosimilar approved by FDA was for Sandoz's Zarxio, the nonproprietary name of which included the suffix -sndz.

And though FDA has said in a proposed rule that it will change the name from "filgrastim-sndz" to "filgrastim-bflm," in addition to changing several others, the agency has gone back and forth on some of the provisions related to the new naming policy.

In June 2016, FDA proposed that sponsors would submit up to 10 proposed suffixes, "in the order of the applicant's preference," with "supporting analyses demonstrating that the proposed suffixes" meet factors described in guidance, though then the agency withdrew that plan.

Regardless of the twists and turns, FDA has made clear that it believes the suffixes are necessary.

"Nonproprietary names that include distinguishing suffixes can serve as a key element to identify specific products in spontaneous adverse event reporting and to reinforce accurate product identification in billing and claims records used for active pharmacovigilance," FDA explained previously. "Other product-specific identifiers, such as proprietary names or NDCs, may not be available or could change over time."