WASHINGTON (CNNMoney.com) - Merck and Schering-Plough fired a shot across Pfizer's bow in the battle for control of the lucrative $25 billion cholesterol market with a new study saying their product is better for diabetics.

Merck (Research), the no. 2 U.S. drug company, and Schering-Plough (Research) released a study Saturday saying that their combination drug Vytorin does a better job at cutting LDL, or "bad" cholesterol, in type 2 diabetics than Pfizer's (Research) Lipitor, the world's top-selling drug from the world's biggest drug company.

In a six-week study involving more than 1,200 patients with the most common type of diabetes, Vytorin, which combines Merck's Zocor with Schering's Zetia, reduced LDL to its medically acceptable goal in 54 percent of patients, according to Dr. Ronald Goldberg of the University of Miami, an independent researcher who led the study that was funded by the two drugmakers. Goldberg said that low doses of Lipitor reduced LDL to the goal in 38 percent of patients and high doses reduced it in 45 percent of patients.

The contrast was greater in the part of the study involving high-risk diabetics, said Goldberg, with Vytorin reducing LDL to its medically acceptable goal 60 percent of the time, compared to Lipitor, which reduced it to the appropriate level 22 percent of the time when taken with low doses and 35 percent of the time with high doses. The study was released at the annual conference of the American Diabetes Association.

Lipitor sales totaled $12.2 billion in 2005, a record high for any drug. Last year, Zocor sales totaled $4.4 billion and the Vytorin tally was $2.4 billion. Zocor loses patent protection on June 23, and Lipitor sales growth has recently slowed, so these companies are looking for ways to increase sales.

Some analysts believe that Lipitor sales could get squeezed by cheaper, generic versions of Zocor after it loses the patent, so Pfizer is working hard to differentiate its product. Pfizer is testing the LDL-lowering Lipitor in conjunction with the experimental drug torcetrapib, which raises HDL, or "good" cholesterol, and according to some analysts this could add billions of dollars in annual sales.

Dr. Rochelle Chaiken, vice president of worldwide medical affairs for Pfizer, said that "what really matters to the clinician and the patient is whether you reduce cardiovascular events." Chaiken said that Lipitor has shown, in clinical studies, that it reduces the incidence of strokes and non-fatal heart attacks by 50 percent in people with diabetes.

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