Drug giant Pfizer has rung down the curtain on the clinical trials and development of its a new generation of drug, torcetrapib, earlier hailed as a strong contender for the replacement of its anti-cholestrol Lipitor after its patent expires in 2011.

Pfizer suspended experiments with the drug abruptly on Saturday after an external panel monitoring the trial reported that clinical trial patients taking the compound in an international experiment, involving 15,000 patients, seemed to have increased the risk of death.

After initial studies showed positive results, Pfizer launched the latest study involving patients at high risk for heart attack and stroke. Half took torcetrapib along with the statin Lipitor; the other half took Lipitor alone.

Of the 15,000 people, 82 who took torcetrapib along with Pfizer's Lipitor died, which was higher than the 51 deaths among those who only took Lipitor.

The drug was supposed to help boost the levels of "good" HDL cholesterol - a new approach in the treatment of heart attacks and strokes. Of the number of new compounds designed to boost HDL levels being studied, torcetrapib was in the most advanced stage of development. These drugs work by inhibiting an enzyme called cholesterol ester transfer protein.

The abandoning of the drug is regarded as a major blow to the drug major as it had already invested an estimated $800 million in drug development, which, if approved, was expected to emerge a blockbuster as early as next year. Only early last week, Pfizer's CEO Jeff Kindler had said that the company hoped torcetrapib could be approved as early as next year.

Pfizer's shares, which closed on Friday at $27.86, with a market capitalisation of $200.88 billion had dropped by over 14 per cent to $23.72 - wiping out $28 billion in market cap.

Last year Lipitor had generated sales of $12.5 billion, one-quarter of the company's $51 billion in annual revenue and nearly half of its net income.

The abandoning of the drug is also a major setback to a key element in medical research for the treatment of Cholestrol, the No. I killer in the US, that of actually boosting the boosting the levels of high-density lipoprotein, the so-called good cholestrol, for reducing the risk of heart attacks and strokes.

So far cholesterol-lowering drugs, called statins have provided an effective treatments for cardiac ailments as they work by lowering the levels of low-density lipoprotein, or LDL, or the "bad" cholesterol. LDL impedes the free flow of blood by clogging the arteries.

Unlike the statin Lipitor, torcetrapib was meant to boost the healthy HDL cholestrol, which experts say remains a promising overall concept. However the news has raised disturbing questions for drug researchers about the most advanced approach, till date, of boosting HDL.

Drug firms have to examine critically similar compounds under development to assess the risk factors associated with their use.

Meanwhile Pfizer has said that it would minutely examine all the data on the drug to determine what had caused the excess risk. Earlier research had indicated that the drug increased blood pressure slightly, but it remained unclear whether that was the problem.

"We now know that the drug did not work, but we do not have a clear answer about why the drug did not work until we see more of the data," said Christie Ballantyne of the Baylor College of Medicine.