Updated from 8:14 a.m. ET with new information.

Alexion Pharmaceuticals (ALXN - Get Report) fired its CEO and chief financial officer Monday amidst an internal probe into allegations of improper sales practices tied to its top-selling drug Soliris.

The Soliris sales investigation, led by Alexion's board, has not identified any facts that require the company to restate previously reported financial results, the company said Monday. Soliris sales have totaled $2.2 billion through the first nine months of the year.

Still, the decision by Alexion's board to sack CEO David Hallal and CFO Vikas Sinha simultaneously certainly suggests the investigation uncovered a serious problem.

At this point, Alexion isn't giving investors any additional information other than to claim that Hallal left the company for "personal reasons." Sinha departs to "pursue other opportunities." Both executives were fired because Alexion's board lost confidence with them, according to CNBC, citing a person familiar with the decision. Alexion held a conference call Monday morning but took no questions from analysts or investors. The Soliris investigation was barely mentioned. 

Alexion shares are down 12% to $115.58 in Monday trading. The stock is down 40% for the year.

David Brennan, a current Alexion board member and former AstraZeneca  (AZO) CEO, takes over as interim CEO immediately, the company said. Sinha is being replaced as CFO with David J. Anderson, the former CFO at Honeywell (HON - Get Report) .

Brennan will receive $6 million in cash compensation to take over as Alexion's interim CEO. The fired Hallal will receive $3.65 million over two years as a parting gift, according to an SEC filing.

The current crisis gripping Alexion began on Nov. 4, when the company cancelled a presentation at a health care investor conference. Rumors that Alexion was an imminent acquisition target turned quickly to concern about the company's delayed 10-Q filing for the third quarter.

Five days later, on Nov. 9, Alexion announced the internal investigation into Soliris sales practices based on an accusation made by a former employee.

On Monday, Alexion said its 10-Q for the third quarter would be filed in January.

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.