Schering-Plough (NYSE: SGP) and Merck (NYSE: MRK) didn't need to hit one out of the ballpark this weekend at the American College of Cardiology (ACC) meeting. All they really needed to do was play solid defense and get out of the inning before a lot of runs got scored on them.

From the reports coming out of the ACC meeting, however, it looks like the drugmakers took a quick beating. The duo apparently couldn't convince doctors that the use of their cholesterol-lowering drugs, Zetia and Vytorin, was still appropriate for most patients.

At the meeting, the drugmakers reported the full data from their Enhance trial, which tested Vytorin, a combination of Zetia and Zocor, against Zocor alone. The full results didn't differ much from the top-line results released in January -- Vytorin still failed to lower plaque in a neck artery more than Zocor, which is available as a cheap generic.

The drugmakers' best hope was to explain why the lack of improvement in plaque buildup doesn't matter, focusing instead on the fact that Vytorin lowers "bad" cholesterol more than Zocor. That's a leading indicator for heart disease -- and what doctors and patients really care about. But it seems that few doctors bought those arguments.

Away from the conference -- although I'm sure competitors with cholesterol drugs the likes of Pfizer (NYSE: PFE), AstraZeneca (NYSE: AZN), and Abbott Laboratories (NYSE: ABT) were happy to point out the news to conference attendees -- the New England Journal of Medicine published two editorials about the Enhance trial, recommending that doctors only use Zetia and Vytorin as a last line of defense.

With today's slide, Merck is off its January high by almost 40%, while Schering has slid nearly 50% from its pre-Enhance high. Given that the drugs make up less than 36% of Merck's adjusted pre-tax income last year, it looks like investors have overreacted by taking away all of the drugs' sales and then some. Schering derives a more substantial amount of its income from the partnership, so the magnitude of its drop may be a little more justified.

Today may be opening day for most baseball teams, but for Merck and Schering, this will be a really long season. Results from the Improve-It trial, which should give a definitive answer on whether the drugs decreased heart-related deaths, won't be available for many years.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.