There was huge disappointment for Merck after a Phase III study of its cholesterol pill Tredaptive failed to hit its targets, casting a shadow of doubt over the drug's future.

As a result, the firm said it will not be seeking approval of Tredaptive (extended-release niacin/laropiprant) in the US, and it stressed that in those countries where it already has regulatory approval doctors should not start new patients on the therapy.

The HPS2-THRIVE (Heart Protection Study 2-Treatment of HDL to Reduce the Incidence of Vascular Events) study of Tredaptive enrolled 25,673 patients considered to be at high risk for cardiovascular events.

It found that adding the pill to statin therapy did not significantly further cut the risk of the combination of coronary deaths, non-fatal heart attacks, strokes or revascularisations.

There was also a statistically significant increase in the incidence of some non-fatal serious side effects in the Tredaptive group, Merck said.

Tredaptive, which boosts levels of high-density lipoprotein, or good cholesterol, pulled in sales of $13 million in the first three quarters of 2012, but analysts had been expecting blockbuster status following a US approval.