Benefit of Merck heart drug remains after stopping

* HDL up, LDL down 8 weeks after stopping anacetrapib

* No adverse safety signals seen with anacetrapib thus far

By Bill Berkrot and Ransdell Pierson

ORLANDO, Fla., Nov 17 (Reuters) - High doses of an experimental heart medicine being developed by Merck & Co(MRK.N) continued to show beneficial effects on both good HDL and bad LDL cholesterol levels eight weeks after patients stopped taking the drug, in a mid-stage study.

The drug, anacetrapib, belongs to a new class of cholesterol treatments called CETP inhibitors that have a checkered past. A similar Pfizer Inc (PFE.N) drug called torcetrapib was one of the most costly and highest-profile failures in pharmaceutical industry history.

Development of the Pfizer drug, which dramatically raised HDL levels, had been halted suddenly due to serious safety issues, including increased deaths.

The new data on the lasting effects of anacetrapib following cessation of therapy were presented on Tuesday at the American Heart Association scientific meeting in Orlando.

"The (anacetrapib) data looks very good thus far and there's no suggestions of the kinds of toxicity that were seen with torcetrapib at this point," Yale Mitchel, Merck's vice president for cardiovascular research, said in an interview.

Mitchel said 800 patients have been treated with the Merck drug for up to 17 months in an ongoing Phase III trial "and there's no evidence of a blood pressure effect or this secondary effect on aldosterone."

An analysis of the torcetrapib data showed it raised blood pressure and unexpectedly altered several blood chemicals, including the hormone aldosterone.

The company had previously issued results of the drug's effects in the 539-patient mid-stage trial that saw LDL reduced 40 percent and HDL increased by a previously unheard of 140 percent at the highest dose.

In the reversal phase of the study, all patients were taken off anacetrapib and followed for eight weeks.

Patients who were taking the highest 300 milligram dose of anacetrapib had HDL increases of 43.4 percent and LDL decreases of 15.3 percent eight weeks after stopping therapy, while at 150 mg, HDL was still up 40.5 percent and LDL down 9.3 percent.

"It's not unexpected that we should see this effect in a drug with a long half-life," Mitchel said.

"On the lower (10 mg and 40 mg) doses, the effects on LDL and HDL were totally gone," Mitchel added.

The company has decided to use a 100 mg dose in its late-stage clinical testing program, noting the U.S. Food and Drug Administration's preference for the lowest possible effective dose.

Given the stunning failure of the Pfizer CETP inhibitor, Merck expects to be required to perform a large, lengthy study to show that its drug actually reduces heart attacks and death rather than just benefits cholesterol levels.

"The plan is to read the data on ongoing trials and if the data looks good we'll initiate a large clinical outcomes study to definitively determine whether the drug is beneficial or not," Mitchel said.

In afternoon trading, Merck shares were up 29 cents or 0.9 percent at $34.10. (Reporting by Bill Berkrot and Ransdell Pierson, editing by Gerald E. McCormick)