Barr Pharmaceuticals ( BRL ) said Friday that it has received tentative government approval for its generic version of Allegra-D, the best-selling allergy drug from France's Aventis ( AVS). The tentative approval reflects the Food and Drug Administration's preliminary determination that a generic product satisfies the substantive requirements for approval, subject to the expiration of legal rights. A tentative approval does not allow the applicant to market the generic drug product. The company said it believes it was the first applicant to file an ANDA containing a Paragraph IV patent challenge on some of the patents relating to the Allegra-D product. If that is the case and if Barr winds up with final approval, it would enjoy a competitive edge as the first to market. New Jersey-based Barr said Aventis had filed a lawsuit seeking to prevent final approval of Barr's drug application until after the expiration of various patents, the last of which expires in 2018. Barr shares ended at $35.10 Thursday.