* Anacetrapib cuts risk to 10.8 pct vs 11.8 pct for placebo
* Drug found to build up in fat tissue
* Merck has not decided whether to seek regulatory approval (Adds analysts' reaction, quote from researcher)
Aug 29 (Reuters) - A large study of a new type of cholesterol medicine from Merck & Co Inc found it cut the risk of heart attack and death by a modest 9 percent, while causing a build up of the drug in fat tissue, leaving its commercial future uncertain.
Researchers, who presented the findings to a medical congress in Barcelona on Tuesday, concluded anacetrapib's efficacy could be due to its affect on bad LDL cholesterol, rather than any more novel action.
Merck said it had not decided whether to seek regulatory approval for the treatment - part of a class known as CETP inhibitors designed to raise HDL, the so-called good cholesterol.
The company announced in June that the study met its main goal, but details have only now been disclosed. It had also previously said that prolonged use of the drug caused accumulation in fat, which may or may not be a problem.
Bernstein analyst Tim Anderson believes it is now unlikely Merck will decide to file anacetrapib for approval, while Berenberg's Alistair Campbell described the results as lackluster.
"It is difficult to see overwhelming physician enthusiasm for anacetrapib," Campbell said.
A little over a decade ago, CETP inhibitors were hailed as the next big heart drug but companies including Pfizer Inc , Eli Lilly and Roche eventually scrapped development programs amid lack of efficacy or safety issues.
Since then, drugmakers have gone on to develop and commercialize another class of cholesterol drugs called PCSK9s.
Merck presented results from its 4-year trial of about 30,000 high-risk heart patients already on statin drugs at the European Society of Cardiology Congress. Statin drugs lower levels of LDL cholesterol.
The study, also published in the New England Journal of Medicine, found that adding anacetrapib to a statin reduced the combined risk of heart attack, heart-related death and need for repeat artery-clearing procedures to 10.8 percent, compared with 11.8 percent for patients on a placebo and a statin.
The trial, led by the University of Oxford and funded by Merck, did not find a significant difference in the risk of ischemic stroke.
The researchers noted that anacetrapib raised blood levels of good cholesterol by a mean of 43 mg per deciliter compared to the placebo. The drug also lowered levels of non-HDL cholesterol by 17 mg per deciliter - a level associated with a 10 percent reduction in the risk of coronary death or heart attack.
"This result reduces the likelihood that other actions of anacetrapib played a major role in modifying the risk of coronary events," researchers concluded.
Martin Landray from Oxford, one of the principal investigators, added: "The large increase in HDL cholesterol levels produced by anacetrapib did not appear to have much impact on risk."
Merck said safety data was generally consistent with earlier trials - anacetrapib patients had slightly higher blood pressure levels than the placebo group - but an analysis showed that the experimental drug accumulates in adipose tissue.
It found that the amount of anacetrapib in fat tissue fell only a small amount a year after treatment ended. Although animal studies have not indicated harm from this, Merck plans a two-year follow up of patients to study long term effects. (Additional reporting by Ben Hirschler; Editing by Mark Potter)