Update: It’s open season on Schering-Plough (SGP). Shares of the drug company plunged 26% in early morning action Monday to a 52-week low after another big setback for Vytorin, the cholesterol drug the company makes with partner Merck (MRK). A panel of heart doctors at the American College of Cardiology conference in Chicago Sunday urged that physicians use other drugs to reduce patients’ cholesterol, after data that showed Vytorin, unlike older drugs called statins, failed to treat heart disease. The decision is likely to lead to a plunge in sales of Vytorin, which combines Schering-Plough’s Zetia with Merck’s Zocor and posted $5 billion in sales last year. A loss of those sales will hit smaller Schering-Plough especially hard, though Merck saw its shares drop 16% just before 10 a.m. The declines at Schering-Plough and Merck are the latest evidence that scientists may not know as much about treating heart disease as they once thought - though statins such as Lipitor emerge from the latest developments largely unscathed. “People need to turn back to statins,” Yale cardiologist Dr. Harlan Krumholz said.

Schering-Plough (SGP) has its hands full defending its handling of a key cholesterol-drug study. The big drug company posted stronger-than-expected fourth-quarter earnings Tuesday morning, saying profits excluding certain costs for the latest quarter rose to 27 cents a share from 17 cents a year earlier. Wall Street analysts had been looking for 25 cents. Schering-Plough’s bottom line in the latest quarter showed a loss of $3.4 billion, or $2.08 a share, tied to its November purchase of Organon Biosciences. CEO Fred Hassan said the integration of that business is on track and added, “The strategic soundness of this combination is clear, and the benefits are becoming increasingly evident.”

Something else that’s plainly evident is that Schering botched the release of the Enhance study that compared its cholesterol-reducing drugs Vytorin and Zetia to a generic version of Merck’s (MRK) Zocor. Its shares have dropped more than 20 percent since last month’s release of that data. As Fortune’s John Simons recently noted, the fact that the costlier drugs worked no better in reducing artery-clogging plaque than an old generic treatment was bad enough. But what was worse was that it took 20 months for Merck and Schering-Plough to acknowledge the new drugs’ shortcomings - a period that saw Zetia sales surge 35 percent.

Yet as CEOs tend to, Hassan sees his company as the victim of unfair expectations. Schering-Plough’s press release notes that “the pharmaceutical industry continues to be subject to ever-more critical scrutiny, where events can be mischaracterized and drive amplified reactions.” That’s one way of saying that investors are starting to hold these companies accountable.