Biotech drug maker Medarex Inc. on Monday said Donald L. Drakeman resigned as president and chief executive immediately, after the release of results from a stock option probe.

Chairman Irwin Lerner was appointed interim president and CEO, and the board launched a search for a new CEO. Lerner was unanimously elected by the board. Drakeman also gave up his seat on the board, along with Michael A. Appelbaum, who also agreed to step down from the board.

An internal probe into the company's stock option accounting practices found that before Sarbanes-Oxley legislation in 2002, it was commonplace for the company to date its stock option grants when shares were trading at relatively low prices, a practice known as "backdating." The company said the probe found no fraud or willful misconduct on the part of management.

Nearly 100 companies are under federal scrutiny, and another 60 have launched internal probes without government prompting.

In June, Medarex said it received a federal grand jury subpoena over the timing of its stock options grants, and had earlier received a letter of informal inquiry from the Securities and Exchange Commission.

At least 41 senior executives or directors, including 11 CEOs, nine finance chiefs and eight general counsels have left at 20 companies following stock option probes.

Senior executives at Medarex involved with the practice have agreed to repay the company any gains from such practices.

Under his employment agreement, Drakeman will remain with the company as an employee until Jan. 4 and as a consultant until March 25 to ensure an orderly transition.

The company is still in the process of restating its financial results from 2000 through 2005 and for the quarter ended March 31, 2006.

Shares of Medarex rose 61 cents, or 5 percent, to $12.80 in afternoon trading on the Nasdaq at above-average volume.