Russia's biggest pharmaceutical company, OAO Pharmstandard, shrunk the most since May 2009 after its plan to buy out unhappy investors' shares at a discount was revealed.

The shares dipped 8.5%, the most in more than four years, on Tuesday's close in Moscow. The trading volume rose to almost 41 times its three-month average. Pharmstandard offered to buy out shareholders who will not vote in favor of a planned spinoff of its over-the-counter business, Pharmstandard said. Pharmstandard cited a board decision in a filing yesterday after Moscow trading closed.

In a phone interview with Bloomberg, Ivan Kushch, an analyst at VTB Capital, said, "This is poor corporate governance practice, they're just trying to get rid of the shareholders on the cheap. This buyout will affect most of the minority shareholders. And those shareholders that don't accept the buyout will be left with the old Pharmstandard shares and a new unlisted and illiquid asset."

Pharmstandard offered the shareholders RUB2,180 a share (US$66).