U.S. drugmaker Merck & Co said it is taking steps to suspend availability of its drug Tredaptive after the medicine, used to raise "good" HDL cholesterol, failed to prevent heart problems in a large study.

The medicine is not approved in the United States but is sold in about 40 countries.

Merck said it is recommending that doctors stop prescribing Tredaptive, based on negative findings from the trial which were announced last month. The study followed more than 25,000 patients in Europe and China for almost four years.

The company said it will encourage doctors to consider alternative treatments to control their cholesterol, but advised patients not to discontinue Tredaptive without first speaking with their physicians.

Merck did not say, in its press release, when it plans to halt shipments of Tredaptive.

Tredaptive combines an extended-release form of niacin with another drug meant to reduce facial flushing, a side effect of niacin. The medicine has annual sales of less than $20 million. That makes it a tiny product for Merck, which has global annual revenue of about $50 billion.

Merck in December said Tredaptive did no better in the study at preventing heart attacks, deaths or strokes than traditional statin drugs that lower "bad" LDL cholesterol.

Moreover, Merck said the medicine significantly raised the incidence of some types of nonfatal but serious side effects in the study. They included blood, lymph and gastrointestinal problems, as well as respiratory and skin issues.

Tredaptive was approved in the European Union in 2008, but the U.S. Food and Drug Administration was unwilling to approve the pill until Merck conducted the costly long-term study to better assess its safety and effectiveness.

Some analysts had expected Tredaptive to capture annual global sales of more than $1 billion, if it were to win approval in the United States.