May 10 (Bloomberg) -- Regulators should demand that Amgen Inc. and Johnson & Johnson put new restrictions in prescribing information for their top-selling anemia drugs, a U.S. advisory panel said today, sending both drugmakers' shares down.

Shares of Amgen fell $5.77, or 9.1 percent, to $57.33 at 4 p.m. New York time in Nasdaq Stock Market composite trading, the biggest drop in more than five years. J&J shares fell $1.61, or 2.5 percent, to $62.50 on the New York Stock Exchange.

The advisory panel to the Food and Drug Administration examined studies that showed the drugs raised the risk of heart attacks, strokes and death when used at high doses. The medicines accounted for $6.6 billion, or 47 percent, of Amgen's revenue in 2006. The FDA warned doctors in March to use the lowest possible doses, and new limits could reduce the company's sales of the drugs by as much as 17 percent, an analyst said.

```The question is how much of the market is going to be restricted,'' said Geoffrey Porges, an analyst with Sanford C. Bernstein in New York, in a telephone interview. ``I would say the panel gave a very strong message to the FDA to take more restrictive action than they have taken already.''

Anemia is a lack of oxygen-carrying red blood cells that produces weakness and fatigue. Epogen and the longer-lasting Aranesp, the drugs made by Amgen of Thousand Oaks, California, are genetically engineered copies of erythropoietin, a protein made by the kidneys that increases the number of red blood cells.

J&J's Version

Johnson & Johnson of New Brunswick, New Jersey, also markets a version of Epogen, called Procrit, which had $3.18 billion in sales in 2006.

The panel of FDA advisers, meeting in Silver Spring, Maryland, didn't spell out what new restrictions should be placed on the drugs, which are approved to fight anemia in people undergoing kidney dialysis and cancer patients in chemotherapy. The agency's options may include a warning that the drugs shouldn't be used for patients with breast cancer and head and neck cancer, based on study results, a panel member said.

``We're telling the FDA that it's OK to look into the possibility,'' said Otis Brawley in an interview after the meeting.

The advisory panel voted 15-2 in favor of new prescribing restrictions, 17-0 for new clinical trials and 11-6 against reducing the maximum recommended dose for the drugs. A reduction in dosage would have been the ``worst-case scenario,'' for Amgen, said Eric Schmidt, an analyst with Cowen & Company, in an interview before the meeting.

The panel also voted 16-1 to recommend that cancer patients stop getting the anemia drugs when their chemotherapy ends and 15-2 to urge that the FDA define how anemic patients should be before they start getting the drug.

The FDA usually follows the recommendations of its advisory panels, although it isn't required to do so.

Companies' Responses

``We will be working with the FDA as they consider the committee's recommendations,'' said Trish Hawkins, an Amgen spokeswoman, in a statement after the meeting.

``When used according to the label, Procrit is safe and effective, and has an acceptable risk/benefit profile,'' J&J said in a statement.

Questions raised by the advisory panel concerned the design of trials, why regulators have limited access to results from company studies and why the drugs have been marketed for improving quality of life if there isn't sufficient evidence for the claim.

`Miracle-Gro for Cancer'

``What data do you have to show me that this is not Miracle- Gro for cancer?'' asked Brawley, a hematologist at Winship Cancer Institute in Bethesda, Maryland. He also asked why Amgen didn't provide full responses to FDA requests for data.

Amgen vice president Roy Baynes replied that academic researchers, like those on the panel, often don't turn over full results to the FDA.

Richard Pazdur, head of the FDA's oncology office, said Amgen had ``an obligation'' to provide full data, considering the safety controversy that arose three years ago, when a similar panel hearing was held.

After the meeting, Brawley said Amgen engaged in ``sleight of hand,'' by trying to avoid answering direct questions. ``They have very aggressively marketed this drug, without doing adequate trials,'' he said in an interview.

``There really has to be more studies,'' Pazdur said at a press conference after the meeting. He said timelines for such studies, and how they should be designed, will be discussed internally at the agency.

Four Million Patients

Four million patients have taken the medicines since they were introduced in 1989, and more than 9,000 people have been studied in clinical trials in cancer patients, according to Amgen.

``We want to consider the totality of the evidence, and consider what's best for patients,'' Roger Perlmutter, Amgen's head of research and development, told the panel at the beginning of the hearing. The anemia drugs don't shorten patients' life spans or make tumors spread more rapidly, based on the findings of 55 studies, he said.

Most of the safety concerns relate to use of the drugs at the higher doses than recommended and to treat conditions for which the FDA hasn't approved them.

The risks were ``clearly demonstrated to be unacceptable'' at high doses, the FDA staff said in an analysis posted May 8 on the agency's Web site. The report cited five studies showing patients died sooner on the anemia drugs than those in a control group.

Head, Neck Cancer

One study in Denmark for an unapproved use, head and neck cancer, showed that patients on high doses of Aranesp had increased tumor growth compared with those on a placebo.

An Amgen-sponsored study of another unapproved use, for cancer patients who aren't on chemotherapy, discovered a higher risk of death. Medicare, the U.S. government health-care program for the elderly and disabled, has since stopped paying for the drug for such patients. The decision could wipe out $500 million a year of Amgen sales, analysts say.

The anemia drugs are usually prescribed in a dose sufficient to boost concentrations of hemoglobin, a protein that carries oxygen in the blood, to 12 grams a deciliter, the FDA-approved level. Some cancer experts have said doctors should use only enough medicine to increase hemoglobin to 10 or 11 grams a deciliter. The advisory panel declined to specify any change to the recommended dose.

Weakening demand for anemia drugs has taken a toll on Amgen. On April 23, Amgen said it would cut expenses to reach the ``low end'' of its $4.30 to $4.50 a share profit forecast for this year.

To contact the reporter on this story: Luke Timmerman in Silver Spring, Maryland ltimmerman@bloomberg.net.

Last Updated: May 10, 2007 18:17 EDT