The first generic versions of Pfizer's antibiotic Zithromax (azithromycin) entered the market Nov. 14 following same-day approval of three companies' ANDAs.

Teva, Sandoz and Pliva each received ANDA approval for azithromycin tablets in three doses - 250 mg, 500 mg and 600 mg.

Teva and Sandoz began shipping Nov. 14. Pfizer's in-house generic division, Greenstone, also concurrently launched generic azithromycin tablets.

The ANDA approvals came 13 days after the Nov. 1 expiration of the azithromycin compound patent.

Zithromax was approved under Section 507 of the FD&C Act; consequently, its patents are not eligible for listing in the "Orange Book" and there is no 180-day generic exclusivity for azithromycin.

However, Pfizer is in litigation with Teva over two azithromycin patents: no. 5,605,889, which covers an oral dosage form of azithromycin that does not exhibit an "adverse food effect," and no. 6,268,489, which covers azithromycin dihydrate. The patents expire in 2014 and 2018, respectively.

The brand company said it does not expect to seek a preliminary injunction to keep the generics off the market.

Pfizer has been preparing for the loss of exclusivity on Zithromax. The company secured FDA approval of the single-dose, sustained-release Zmax in June (¹ Also see "Pfizer Zmax Approved For One-Dose-Only Antibiotic Therapy" - Pink Sheet, 13 June, 2005.).

The firm's sales force stopped actively promoting Zithromax in July, with reps shifting to Zmax promotion.

Pfizer reported U.S. Zithromax sales of $1.39 bil. in 2004.

-Sue Sutter

Pfizer’s Zithromax Gets Generic Competition Following ANDA Approvals

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