(Bloomberg)—GlaxoSmithKline P.L.C., the U.K.’s biggest drugmaker, said it will have fourth-quarter legal costs of £2.2 billion ($3.49 billion) because of a U.S. investigation into sales practices for certain products and product liability cases related to the Avandia diabetes drug.

The company is setting aside additional provisions for the investigation by the U.S. attorney in Colorado into the company’s sales and promotional practices of certain products, London-based Glaxo said in an e-mailed statement Monday. The money also will cover for the “substantial” number of new claims filed in the U.S. regarding Avandia, Glaxo said.

Today’s charge brings to £4 billion ($6.35 billion) the amount Glaxo set aside for possible legal costs in 2010. While all companies have costs for litigation, the size of Glaxo’s charges is unusual, said Navid Malik, an analyst with Matrix Corporate Capital L.L.P. in London.

“I am a bit surprised to see such a high charge come in,” Malik said in a telephone interview Monday. “I thought there was going to be an additional charge, but I didn’t think it was going to be this high.”

GlaxoSmithKline shares fell 20 pence (31.7 cents), or 1.6 percent, to 1,205 pence ($1.91) at the close of trading in London, erasing earlier gains of as much as 1.4 percent.

The company said Sept. 23 it would stop promoting Avandia worldwide after regulators said the treatment would be withdrawn from the market in Europe and sales would be limited in the U.S. because of an increased risk of heart attacks. Avandia was once the world’s best-selling diabetes drug.

The expense announced today will be £1.8 billion ($2.86 billion) after taxes, Glaxo said. Analysts estimated the company would earn £1.44 billion ($2.29 billion) excluding some items in the fourth quarter, meaning Glaxo is now likely to report a quarterly loss.

“We recognize that this is a significant charge, but we believe the approach we are taking to resolve long-standing legal matter is in the company’s best interest,” PD Villarreal, Glaxo’s senior vp of litigation, said in Monday’s statement. “We have closed out a number of major cases over the last year and we remain determined to do all we can to reduce our litigation risk.”