Friday, November 19, 2004

Anchen files ANDA for Wellbutrin XL (buproprion)

Taiwan-based generic company Anchen Pharmaceuticals has submitted an abbreviated new drug application (ANDA) to the FDA for Biovail's Wellbutrin XL (once daily dose of bupropion for depression).

Litigation over bupropion has been extensive. Current issues are NOT about the drug itself (the composition of which is off patent) but about the formulations for controlled delivery of the drug. The Excel and Impax decisions of the Court of Appeals for the Federal Circuit have involved interpretation of the foreseeability prong of the US Supreme Court decision in Festo (535 US 722 (2002)).

Wellbutrin is a drug used to treat depression, but the underlying chemical is also used for smoking cessation (marketed as ZYBAN). Of depression, the chemical is different from Paxil, Prozac and Zoloft, and as a result, Wellbutrin can often successfully treat people with depression whose condition has not improved from taking these other drugs.

Although the chemical of Wellbutrin and Zyban has been off patent as a composition of matter for a long time, in 1995 Glaxo received a patent for the extended release formula of Wellbutrin SR. In 1999, generic drug manufacturer Andrx filed two ANDAs with the FDA seeking to sell generic versions of extended release Wellbutrin and Zyban. Andrx argued that because its generic used a different method of extended release, that it did not infringe on Glaxo's patent. Four other generic manufacturers followed Andrx's lead, and several have received tentative approval to manufacture and market their generic versions. In February of 2002, the US District Court for the Southern District of Florida ruled that Andrx did not violate Glaxo’s patent and therefore should be allowed to manufacture and market its generics. On appeal, however, the Federal Circuit Court of Appeals held that the district court in Florida erred in its construction of the patent infringement claims.

Glaxo owns U.S. Patent No. 5,427,798 (the ’798 patent) directed to controlled sustained release tablets containing bupropion hydrochloride. Pharmacologically, bupropion (m-chloro--t-butylaminopropiophenone) is a monocyclic aminoketone antidepressant. See U.S. Patent No. 4,393,078 (issued July 12, 1983) (the ’078 patent). These compounds treat depression and inebriation. In addition, they facilitate the cessation of smoking by producing neural stimulation in mammalian systems. See ’798 patent, col. 1, ll. 5-10; ’078 patent, col. 1, ll. 29-39; U.S. Patent No. 3,819,706 (issued June 23, 1974). To avoid the need for multiple dosages with the attendant fluctuations in plasma bupropion concentrations, Glaxo invented a sustained release formulation of the compound. While bupropion hydrochloride itself was separately patented, Glaxo obtained the ’798 patent to protect its sustained release formulation of the drug. Glaxo markets this patented sustained release formulation as Wellbutrin®SR for treatment of depression and as Zyban® for smoking cessation. The key ingredient for achieving sustained release in this invention is hydroxypropyl methylcellulose (HPMC), which is a partly O-methylated and O-(2-hydroxypropylated) cellulose. In oral preparations, HPMC extends drug release by transforming into a gel that swells upon ingestion. The hydrogel state of HPMC releases bupropion hydrochloride from an ingested tablet over a period of time.

The ’798 patent claims a sustained release tablet containing an admixture of bupropion hydrochloride and HPMC. However, many of the claims as originally filed did not recite HPMC as a limitation. During prosecution on the merits in the United States Patent and Trademark Office (Patent Office), the examiner rejected the claims that did not recite HPMC for lack of enablement under 35 U.S.C. § 112, 1. Glaxo amended those claims to overcome the rejection.

The first independent claim of the ’798 patent states:

1. A controlled release tablet comprising 25 to 500 mg of bupropion hydrochloride and hydroxypropyl methylcellulose, the amount of hydroxypropyl methylcellulose to one part bupropion hydrochloride being 0.19 to 1.1 and said tablet having a surface to volume ratio of 3:1 to 25:1 cm-1 and said tablet having a shelf life of at least one year at 59deg to 77deg F. and 35 to 60% relative humidity, said tablet releasing between about 20 and 60 percent of bupropion hydrochloride in water in 1 hour, between about 50 and 90 percent in 4 hours and not less than about 75 percent less in 8 hours.

3 Comments:

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