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Abbott Labs (NYSE:ABT) is fending off multiple generic challenges to Biaxin XL (clarithromycin extended-release tablets), an antibiotic with annual sales of over $300 million in the United States. Companies that have filed ANDAs for generic versions of Biaxin XL include Ranbaxy, Teva (NYSE:TEVA), Andrx, Roxane, and Sandoz.

In Abbott's case against Teva, Abbott lost a motion for a preliminary injunction on grounds that its patents on Biaxin XL were likely invalid. Shortly after the Federal Circuit affirmed that decision, Abbott and Teva reached a settlement. In Abbott's case against Ranbaxy, the district court held that two of Abbott's patents were likely unenforceable. Now, in an unanimous opinion released last Friday, the Federal Circuit has affirmed a preliminary injunction that Abbott won against Andrx.

On appeal, Andrx presented two main arguments: (1) based on the findings made in Abbott's cases against Teva and Ranbaxy, Abbott was collaterally estopped from asserting the patents in suit against Andrx; and (2) given the district court's construction of the claim term "pharmaceutically acceptable polymer," Andrx's generic version of Biaxin XL does not infringe the claims under the doctrine of equivalents.
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With regard to Andrx's first argument, the Federal Circuit found that in the Teva and Ranbaxy cases, "the district court judge did not intend to 'firmly and finally resolve the issue' for which preclusion is asserted," as required by the Supreme Court's Blonder-Tongue decision. Furthermore, the court found that this case did not "present the rare circumstance in which a determination made during a preliminary injunction is sufficiently final to be accorded preclusive effect." Therefore, the court held that Abbott was not collaterally estopped from asserting the patents in suit against Andrx.

In addressing Andrx's noninfringement argument, the Federal Circuit first reviewed the district court's construction of the claim term "pharmaceutically acceptable polymer." The court found that the district court construed this term too narrowly, in part because it read Markush group language from the specification into the claim. The term 'Markush group' does not have any meaning within the context of a written description of a patent and therefore, to the extent the district court relied on the Markush group language to limit its construction to the compounds listed in the written description, it erred.

The court then proceeded to reject Andrx's noninfringement position, which was based on the "specific exclusion principle" and the "doctrine of claim vitiation." Accordingly, the court found that Andrx's generic Biaxin XL formulation could be shown to be equivalent to Abbott's claimed formulation.

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Source: Abbott Fighting Challenges to Antibiotic