In typical fashion, Roy Poses at Health Care Renewal is all over this. He quotes this from a recent WSJ article (my italics):
WASHINGTON—A medical researcher and two medical groups with financial ties to Sanofi-Aventis SA have asked federal regulators to hold off on approving generic forms of a Sanofi blood-thinner, the latest twist in a long running battle to market generic versions of a drug with annual sales topping $4 billion.
Citing potential patient safety issues, the head of the Society of Hospital Medicine and a medical researcher at Duke University last month sent letters to the Food and Drug Administration contending that Lovenox is too complex for any generic maker to copy fully.
Too complex to copy fully? I'm no expert in pharmacology but that's a novel argument to me. Yes, I'm sure the manufacturing process is complex. And yes, any variation in potency, particularly for an anticoagulant, especially one whose biological effect cannot be monitored readily in most hospitals, could be a critical patient safety issue. The issue of potency variation in generic drugs has been raised before, for drugs such as thyroxine. A generic drug does not have to prove efficacy and safety to get approved, only bioequivalence. For some drugs the FDA's bioequivalence standards permit variation in potency on the order of 25% form the brand name drug. This could be highly significant for drugs with a narrow therapeutic window, particularly those like Lovenox where the biologic effect cannot be easily monitored.
I don't know if that's the concern here, but it's plausible. As a member of SHM, I hope they explain.