As rival multiple sclerosis drug Tysabri is poised to come back into the market, analysts aren't very concerned over the potential renewed threat to Teva Pharmaceutical Industries Ltd.'s competing Copaxone product. "Tysabri's return to the shelves is a non-event. It will only be given to patients as a last resort, in cases in which Copaxone would not work," said Richard Gussow, senior analyst at Excellence Nessuah. Tysabri, produced by Ireland's Elan Corp. and Biogen Idec, was given first approval by a US Food and Drug Administration panel to return to the market earlier this week. The drug had been hailed as a potential blockbuster treatment for multiple sclerosis with annual sales of $3 billion, before it was removed from the market last spring after three patients who had been using the drug contracted a rare brain disease called progressive multifocal leukoencephalopathy (PML). The FDA is expected to make a final decision on reinstating Tysabri by the end of the month. "It's not great news for Teva, but Tysabri's potential to win market share in the MS market is very limited. Patients and doctors will be very cautious about a drug that was associated with PML related deaths," said Ori Hershkovits, analyst at Leader & Co. Hershkovits added that even if Tysabri would reach annual sales of $1b. at best in the $4b. MS market, Teva's Copaxone still covered 30 percent of the market. "At the most Tysabri might slow down the sales growth of Copaxone," Hershkovits said. Separately, AstraZeneca, the anglo-Swedish drugmaker filed a lawsuit against Ivax Corp. which was acquired by Teva earlier this year, to halt a generic version of its ulcer drug Nexium, the company's top selling product. "This is a common tactic being used by drug companies to delay the launch of generic drugs in an effort to delay the interference with their sales," said Gussow. The filing automatically blocks US drug regulators from approving Teva's version of the medicine until a US court rules on the dispute or for 30 months, whichever is the shorter period. AstraZeneca claims that Ivax was trying to bring to the market a generic form of Nexium in the United States prior to the expiration of five AstraZeneca patents. In the lawsuit, filed in the US District Court of New Jersey, AstraZeneca said the expiration dates for the respective patents ranged from 2014 to 2019. Nexium generated $4.6b. in sales in 2005. At the end of last year London-based AstraZeneca also commenced patent infringement litigation regarding Teva's attempt to market a generic version of the schizophrenia drug Seroquel, the company's second biggest product.