* Accused of patent infringement related to tramadol
* Shares down 21.6 percent
TORONTO, Nov 2 (Reuters) - Cipher Pharmaceuticals Inc DND.TO said on Monday that two drug companies have accused it of violating a U.S. drug patent, knocking the shares of the small Canadian drugmaker down by more than 20 percent.
The company said Purdue Pharma Products and Napp Pharmaceutical Group filed a complaint in a Virginia court related to a new drug application Cipher filed with the U.S. Food and Drug Administration for its extended-release tramadol pain treatment.
Toronto-based Cipher filed a revised new drug application for tramadol in the second quarter of 2008, and received tentative approval from the FDA in February 2009.
The company’s lightly traded stock was down 21.6 percent at 45.5 Canadian cents on the Toronto Stock Exchange on a volume of 2,000 shares.
Cipher said in a release that it “intends to vigorously defend itself against the suit and is confident in the strength of its application.”
$1=$1.07 Canadian Reporting by Scott Anderson; editing by Rob Wilson