Would you please clarify what you mean by "substitutable" vs. "non-substitutable" FOB. I'm not familiar with that term.
A substitutable (or interchangeable) FoB is one that can be issued by a pharmacist to fill a prescription for the corresponding branded drug; thus, a substitutable FoB need not be actively marketed to obtain market share. A non-substitutable FoB, on the other hand, is a distinct drug for sales and marketing purposes.
Although Lovenox is not considered a biologic and it was approved under the FDA regulations for generic versions of small-molecule drugs, it works the same way in the marketplace as a substitutable FoB.
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