<<I respectfully disagree with your assertion that the holding was not justified under the bioequivalence clause 355(j)(2)(a)(iv).>>
We are in agreement about the judge's reasoning in general. If the immunogenicity tests were necessary to prove bioequivalence, I think the judge would have said the statute permits the FDA to require the tests. But I don't think that is what bioequivalence means, purity and lack of immune response are not relevant for bioequivalence as the FDA appears to define it. See "Guidance for Industry Bioavailability and Bioequivalence Studies for Orally Administered Drug Products — General Considerations" at http://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/ucm070124.pdf, which quotes from interpretative regulations and provdes the following defintion:
Bioequivalence is defined in § 320.1 as: the absence of a significant difference in the rate and extent to which the active ingredient or active moiety in pharmaceutical equivalents or pharmaceutical alternatives becomes available at the site of drug action when administered at the same molar dose under similar conditions in an appropriately designed study.
The Guidance describes on pages 6 - 9 the types of studies that prove bioequivalence.