* TSX ends down 137.73 points, or 1 percent, at 13,704.19
* Seven of the TSX's 10 main groups fall
By Alastair Sharp
TORONTO, Oct 21 (Reuters) - A plunge in shares of Valeant Pharmaceuticals International Inc helped push Canada's main stock index down 1 percent on Wednesday, with falls in the price of oil and other commodities weighing on energy and mining stocks.
Valeant slid 19.2 percent to C$154.21 after an influential short-seller accused the company of using specialty pharmacies to inflate its revenue, an allegation the drugmaker denied. It fell as much as 40 percent during the session.
After Valeant, 23 of the next 25 most influential decliners were either energy or materials stocks.
The other top non-resource weight was technology company Celestica Inc, which fell 15.2 percent to C$14.45 after its earnings and outlook missed expectations.
"This market is getting more difficult to move on," said Kevin Headland, a director of capital markets and strategy at Manulife Asset Management.
"Based on North American valuations, the S&P 500 and TSX - valuations are fair to high. You have to look at specific individual companies and try to unearth some value there."
The energy group retreated 3.3 percent and materials, which includes miners, retreated 2.5 percent.
Oil prices slid 2 percent to a three-week low as U.S. crude inventories grew, while weak demand from China weighed on prices for copper and iron ore.
The Toronto Stock Exchange's S&P/TSX composite index ended down 137.73 points, or 1.00 percent, at 13,704.19, with seven of its 10 main groups lower and the influential financials sector flat.
"I'd expect a flat market between here and the end of the year," Headland said, citing little impetus for heavyweight energy, mining and financial stocks to move higher.
The most influential gainers included telecom companies BCE Inc, which rose 1.2 percent to C$58.22, and Telus Corp , which added 1.3 percent to C$43.47. (Reporting by Alastair Sharp; Editing by Nick Zieminski and David Gregorio)