Pfizer has settled its lawsuit against Novartis for alleged infringement of the US patent for the antibiotic Zithromax (azithromycin), Bloomberg News reports.

Pfizer first sued Novartis and its Sandoz generics unit in February 2006 in federal court in Wilmington, DE.

Pfizer sought unspecified damages in the case, stating it would be “irreparably harmed” by Novartis’ use of a formulation of crystal azithromycin. Under the settlement, Pfizer and Novartis “have agreed to settle all claims” regarding the drug patent, court documents said.

The settlement is Pfizer’s second in a year related to the Zithromax patent. In November of 2006, Israel’s Teva Pharmaceutical Industries said it would pay Pfizer as much as $70 million for rights to make copies of Zithromax and cancer drug Idamycin.

Pfizer has seen sales of Zithromax nosedive as the other drugmakers, including American Pharmaceutical Partners, were able to bring their versions of azithromycin to market following the expiration of the drug’s US patent in 2005.

Branded Zithromax had $638 million in sales in 2006, down from $2 billion in 2005.