Merck (NYSE: MRK) may have Vytorin 2.0 on its hands.

Multibillion-dollar Vytorin lowered bad cholesterol levels well, helping it compete with statins like Pfizer's (NYSE: PFE) Lipitor or AstraZeneca's (NYSE: AZN) Crestor. But Merck has failed to show that the lower cholesterol level translated into a decrease in the plaque in the arteries, and sales have sunk.

The new drug, anacetrapib, could have equally strong sales, but it's not without risk. Rather than just lowering bad cholesterol, the main job of anacetrapib is to raise good cholesterol. Good cholesterol cleans fats out of the arteries, which should help reduce the incidence of heart attacks and strokes.

Anacetrapib seems to work pretty well. Data from a phase 3 trial showed a 40% drop in bad cholesterol and a 138% increase in the good cholesterol for patients taking anacetrapib. Those are some pretty remarkable numbers.

The problem is that Pfizer's torcetrapib, which is in the same class of drugs, looked promising as well. But it exploded in phase 3 trials when it became clear patients taking the drug were dying at a higher rate than those taking placebo.

Anacetrapib doesn't seem to have the same issues -- increased blood pressure, electrolytes, and the hormone aldosterone -- that led to the increase in deaths, but I'm not sure 1,623 patients in a 18-month study is a large enough sample size to really rule out all the potential problems. Merck plans to start a 30,000-patient trial next year. That'll be the true test of whether torcetrapib was a fluke or whether the entire class of drugs is tarnished.

Roche and Eli Lilly (NYSE: LLY) have drugs in the same class. Usually a company would be rooting against its competitor, but I have to think Roche and Eli Lilly would prefer to see anacetrapib work and hope their drugs are better than to see side effects for anacetrapib crop up in a larger study.

Today's news is certainly good for Merck, but investors should be careful translating that news into future revenue. Anacetrapib is still far from being on the market, and a lot can happen in that time.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Fool has a disclosure policy.