Merck & Co is debating the significance of a study which suggests that Abbott Laboratories' Niaspan is more effective than the New Jersey-based major’s Zetia in terms of preventing clogged arteries.

Eagerly-awaited results from the ARBITER 6 - HALTS study, which was terminated early in July, are being presented at the American Heart Association meeting in Orlando. The 208-patient trial showed patients at high cardiovascular risk had significant regression of atherosclerosis after eight and 14 months of therapy with Niaspan (extended-release niacin) plus a statin, the study's primary endpoint. However, in a pre-specified secondary endpoint, treatment with Niaspan plus statin also resulted in “significantly fewer major adverse cardiac events” as compared to Zetia (ezetimibe) plus a statin, Abbott noted.

Eugene Sun, vice president of global pharmaceutical development at Abbott, said the study is the first study showing that HDL-raising with Niaspan on top of statin regresses atherosclerosis compared to an LDL-lowering strategy, ie using Zetia. He added that "these data reinforce the importance of looking beyond LDL treatment targets to address other lipid parameters." The results have led some observers to claim that this is another blow for Merck, given the controversy already surrounding Zetia and Vytorin, which combines ezetimibe and simvastatin, as the two treatments have been under the spotlight since the negative findings of ENHANCE study last year, coupled with the handling of the data.

However Peter Kim, president of Merck Research Laboratories, said that “nothing from this study, which a New England Journal of Medicine editorial says has 'several limitations,' changes the well-established understanding that lowering LDL cholesterol is the primary target of therapy according to the guidelines”. He added that the results were “widely predicted” because its design favoured niacin as the patient population selected had well-controlled LDL cholesterol and relatively low HDL cholesterol.

Dr Kim went on to say that ARBITER 6 “is not an outcomes study, and does not have the rigour or size to provide meaningful insight into the effect of either niacin or ezetimibe on clinical outcomes. He went on to say that Merck has reviewed the data from 43 completed shorter-term trials involving 2,400 patients who received ezetimibe alone and 13,600 patients who received ezetimibe with statins, as well as two longer-term studies. As such, the firm is “confident that the data support the safety profiles of Zetia and Vytorin as described in their labels”.

Dr Kim concluded by saying that "any suggestion that the results of ARBITER 6 can definitively answer the question of the impact of ezetimibe on cardiovascular outcomes or that its results have implications for clinical use should be met with scepticism”.