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In Reply Drs Frankel and McKay first note that the FDA is able to ensure biosimilar and reference biologic quality through prerelease specifications. But these specifications cover only a subset of all measurable quality attributes. If FDA testing were adequate to predict all emergent quality-related safety issues with biologics, then there never would have been cases of pure red blood cell aplasia associated with Eprex1 or HX575, which are biosimilar versions of epoetin-α, nor would have there have been deaths due to contaminated heparin in the United States in 2008.2
Chandra A, Vanderpuye-Orgle J. Competition and Biosimilar Products—Reply. JAMA. 2015;314(24):2692. doi:10.1001/jama.2015.15058