FDA Approves Teva's Generic Lexapro; Patent Case Still Pending in District Court

Teva announced Monday that the FDA has granted final approval of generic Lexapro to Teva's IVAX unit.  Lexapro, manufactured by Forest Laboratories, is a selective serotonin reuptake inhibitor (SSRI) antidepressant, with annual sales of over $2 billion in the United States.  Lexapro sales account for 60% of Forest's revenue.

Forest Labs' patent infringement case against IVAX concerning IVAX's ANDA for generic Lexapro is still pending before Judge Farnan in the U.S. District Court for the District of Delaware.  See Forest Labs. v. IVAX Pharms., No. 03-891.  A bench trial was held in March, and post-trial briefing was completed last week.  Teva has not announced whether it intends to launch generic Lexapro at risk.

In the patent case, Forest alleges that IVAX's ANDA for generic Lexapro infringes U.S. Pat. No. Re. 34,712, which is a reissue patent of U.S. Pat. No. 4,943,590.  The '712 patent claims substantially pure (+)-citalopram, the active ingredient in Lexapro, also known as "S-citalopram" or "escitalopram."  (+)-citalopram is also the active ingredient in Forest's older generation SSRI, Celexa, which is a racemic mixture of (+) and (-) citalopram.  The patents on Celexa have expired.  According to the Orange Book, the '712 patent will not expire until June, 2009.  [Update:  An alert reader just informed me that Forest was recently granted a patent term extension.  The '712 patent is now set to expire in March, 2012.  Forest announced the extension in a recent press release.]

In its post-trial brief, IVAX argues that the '712 patent is invalid for anticipation and obviousness, invalid for broadening reissue, and unenforceable for inequitable conduct.  In its lead argument, IVAX argues that a prior art reference, Smith, describes (+) and (-) citalopram as individual enantiomers in a form separated from each other.  Forest counters in its post-trial brief that Smith does not anticipate the '712 patent because it does not enable one of skill in the art to make substantially pure (+)-citalopram without undue experimentation.

Based on prior experience with Judge Farnan, a decision in the case may not be announced for six months to a year.