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ZENITH’s GENERIC CEFADROXIL APPROVED BUT PATENT SUIT REMAINS UNRESOLVED

Executive Summary

ZENITH's GENERIC CEFADROXIL APPROVED BUT PATENT SUIT REMAINS UNRESOLVED, delaying the product launch. Northvale-N.J.-based Zenith Laboratories announced April 22 that FDA approved its ANDA supplement for the antibiotic. No generic version of Bristol-Myers Squibb's Duricef has been marketed since 1990. However, the long- running patent infringement suit between the two firms returns to trial May 18 in Newark Federal Court. Zenith also lacks a bulk ingredient supplier for the product. It has been in negotiations with Gema, a Spanish subsidiary of Sandoz, with which Zenith previously had a supply agreement. Gema withdrew from the arrangement in September 1991 after BMS filed a patent infringement suit against Sandoz. The resumption of the patent trial follows an April 13 ruling by the federal court. The court accepted BMS' motion for reconsideration, vacating a Feb. 21 summary judgment in favor of Zenith ("The Pink Sheet" March 2, T&G-2). The BMS motion cited additional evidence that the court did not consider before issuing the summary judgment. The BMS contention that "the court should have exercised its discretion and proceeded cautiously before granting summary judgment is well taken," the court said in ordering a return to trial. In the earlier round, BMS claimed that Zenith's cefadroxil DC converts into the Bristol antibiotic product in the stomach and also submitted expert declarations and experimental evidence that cefadroxil DC converts to the BMS product when mixed with water. Zenith had presented evidence that the Bristol studies were unlike conditions in the stomach and thus "shed insufficient light on the conversion question to raise a genuine issue," the court declared in February. The court at that time did not consider certain expert testimony that BMS submitted after a court hearing but before the Feb. 21 ruling. That testimony "explains Bristol's theory clearly and also provides evidence based on tests designed to simulate in vivo conditions," the court explains in its April 13 order. On April 6, FDA Center for Drug Evaluation and Research Director Carl Peck, MD, informed BMS that FDA is denying its July 13, 1990 petition requesting that the agency deny approval of Zenith's and Gema's cefadroxil applications. BMS contends that the generic cefadroxil is not a monohydrate and therefore does not comply with the standards in FDA's monograph for the drug substance. Peck noted that FDA has determined that the drug manufactured by Gema is a hemihydrate, which differs from the monograph only in its water of hydration. Peck stated: "FDA considers differences in waters of hydration resulting in polymorphic crystal forms of the same active moiety (i.e., different forms of the same active ingredient) to be the same when dissolution, solubility, and absorption are shown to be equivalent." The FDAer pointed out that "cefadroxil hemihydrate is neither a salt nor an ester of cefadroxil monohydrate. The active moiety of each ingredient is cefadroxil." He added: "Therefore, a cefadroxil hemihydrate product would be considered a 'duplicate' of a cefadroxil monohydrate product." The agency "may accept and approve an abbreviated antibiotic application for cefadroxil hemihydrate if the applicant can meet all of the standards of the monohydrate monograph except the moisture content specification, and the applicant shows that its product is bioequivalent to the cefadroxil monohydrate product."

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