Untested diet drug combination concerns researchers

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May 19, 1999
Web posted at: 2:08 p.m. EDT (1808 GMT)

(CNN) -- A new combination of drugs being prescribed for weight loss has some researchers concerned. It reminds them of the popular combination of two years ago, fen-phen, that resulted in serious health problems for many of its users.

Xen-phen is the combination of Xenical and phentermine. Xenical is new to the marketplace. Since its release just three weeks ago, more than 49,000 prescriptions have been written, and it is available over the Internet. Some doctors have started prescribing the new drug in combination with another drug called phentermine.

The previous weight loss combination, fen-phen, brought together fenfluramine and phentermine. Fenfluramine was removed from the market almost two years ago after it was linked to heart valve problems, but phentermine remains available.

Xen-phen worries Dr. Pamela Peeke of the National Institutes of Health.

"This is exactly what happened with phentermine and fenfluramine -- and that is phentermine had been on the market for a long time, and it was added with fenfluramine. The real key here, more than anything else, is that you have someone who watches you carefully and fully discloses the fact that these have not been studied together," Peeke said.

Xenical works as a fat blocker. Dr. James Biggers acknowledged the lack of studies on the Xen-phen combination but said the drugs work differently. While Xenical blocks about a third of the dietary fat in the gastrointestinal tract, phentermine may suppress appetite by working on the brain.

"Because of the distant focus of action or mode of action, it would seem reasonable that these drugs would be safe to be used together," Biggers said.

How widely Xen-phen is used is not known. Used alone, Xenical results in a five to 10 percent weight loss per year, and it must be taken with a low-fat diet. The untested combination may tempt some doctors and patients to try to accelerate weight loss.

Medical Correspondent Linda Ciampa contributed to this report.