Shares of Mylan Laboratories ( MYL) rose Tuesday after the company said it received government approval to sell a generic version of Pfizer's ( PFE) blockbuster blood pressure drug Norvasc. The Food and Drug Administration's approval could mean big money for Mylan, because Norvasc produced $4.4 billion in worldwide sales (including $2 billion in the U.S.) last year. Under FDA rules, the first company to file a successful generic application gets 180 days of market exclusivity once a brand-name drug's patent expires. Mylan's shares gained $1.29, or 6.7%, to $20.67, exceeding its 52-week high. A company spokesman declined to say when Mylan would begin selling the generic drug, which still faces a few potential hurdles. Pfizer and Mylan are entwined in a patent infringement lawsuit over Norvasc, whose patent expires in early 2007. The FDA said the 180-day exclusivity period will start "from the earlier of the commercial launch of the Mylan product or a final decision concerning the pending litigation," according to Mylan. "Given the uncertainty of the patent litigation, we have not included contribution from generic Norvasc in our current Mylan model," Michael Tong of Wachovia Securities wrote in a Tuesday report to clients. Tong said the companies could try to settle their differences or continue to fight in court. Or, Mylan could make an "at risk" launch immediately, hoping that it wins in court. If Mylan loses, the financial penalty would be severe. The 180-day exclusivity period could be worth 28 cents a share to Mylan, Tong believes. He has a market-perform rating on Mylan. He added that at least four other generic manufacturers have applications pending before the FDA for generic Norvasc. Tong doesn't own shares of Mylan, and his firm says it intends to receive or seek investment-banking-related compensation in the next three months.