Niaspan tops Zetia in new setback for Merck drug

* Niaspan leads to reduction in artery wall thickness

* No meaningful change seen with Zetia

* 5 times as many serious adverse events seen with Zetia

* Journal editorials cite several limitations of study

ORLANDO, Nov 15 (Reuters) - Abbott Laboratories' (ABT.N) Niaspan appeared to be more effective and safer than Merck & Co's (MRK.N) Zetia as a secondary cholesterol treatment, according to a small study released on Sunday that is likely to further tarnish Merck's damaged cholesterol franchise.

The damage, however, may be limited by the limitations of the study itself, which included data from just 208 patients and was criticized in a major medical journal.

"Niacin is the clear winner and led to very clear reductions in the amount of atherosclerosis that patients had," Alan Taylor, the study's lead investigator who will present the data on Monday at the American Heart Association scientific meeting in Orlando, said in an interview.

The study tested the effect on carotid artery wall thickness of adding either Niaspan, a long-acting niacin that raises good HDL cholesterol, or Zetia, which lowers bad LDL levels. It involved patients who had heart disease or high risk of heart disease whose LDL was already at target levels from taking statins -- the first-line treatment for high cholesterol -- but who had low HDL levels.

Increases in thickness of the artery wall could be an indicator of build-up of dangerous plaque that causes atherosclerosis and can lead to heart attacks, while a decrease could indicate regression of the disease. (Reporting by Bill Berkrot and Ransdell Pierson; Editing by Leslie Adler)