US patent office to review Bristol/Sanofi's Plavix

* Canada’s Apotex requested review

* Courts have upheld patent’s validity

NEW YORK, Aug 18 (Reuters) - U.S. patent officials have agreed to review the patent governing Plavix, the blood-clot treatment sold by Bristol-Myers Squibb BMY.N and Sanofi-Aventis SASY.PA, a Bristol spokeswoman confirmed on Tuesday.

Canada-based Apotex, which has long fought Bristol and Sanofi in a bid to sell generic versions of Plavix, had asked the U.S. Patent and Trademark Office to review the patent, Bristol spokeswoman Laura Hortas said.

The composition-of-matter patent governing Plavix is expected to expire in November 2011, although the companies might win a six-month extension for conducting pediatric studies.

The U.S. Court of Appeals for the Federal Circuit in December upheld a ruling supporting the validity of the patent. The ruling backed a decision by the District Court for the Southern District of New York.

“At this stage, the Plavix patent remains valid and enforceable, the court injunction remains in effect and we are confident in the validity of the patent, which was thoroughly examined by the District Court and Court of Appeals,” Hortas said.

Bristol shares closed up 10 cents at $21.77 on the New York Stock Exchange. Sanofi’s U.S.-traded shares fell 2 cents to $31.70 on the New York Stock Exchange. (Reporting by Lewis Krauskopf. Editing by Robert MacMillan)