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Merck's New Obesity Drug Cuts Pounds

Posted: Tuesday, January 15, 2008

An experimental Merck obesity drug helped patients lose weight and burn up calories, but at higher doses caused psychiatric side effects similar to those that prevented U.S. approval of a similar Sanofi-Aventis drug, researchers said.

The findings, seen in mid-stage trials of Merck's taranabant, were reported in the January issue of the journal Cell Metabolism. The pill is currently being tested in a far larger late-stage trial whose results are expected to be unveiled later this year.

Taranabant, like Sanofi-Aventis' rejected ribonabant, works by blocking cannabinoid receptors in the brain. They are the same receptors that make people hungry when smoking marijuana.

"When you block the cannabinoid system with an antagonist like taranabant, you suppress appetite," said Steven Heymsfield, a Merck executive who helped conduct the studies.

One of the Phase II trials involved 553 obese patients who were tested for 12 weeks. They were divided into groups that received different daily doses of taranabant -- ranging from 0.5 milligram to 6 milligrams -- or placebos.

Patients receiving the Merck drug lost 8 to 14 pounds of body weight. Researchers said that compared favorably with weight losses seen in separate and far longer late-stage trials of rimonabant, which is sold in some overseas markets.

But the article said the weight-loss benefit of taranabant must be weighed against side effects of the Merck pill, especially psychiatric problems "reminiscent" of those seen with ribonabant -- such as depression, anxiety and irritability.

"Although the trends in these and related factors were small and not statistically reliable, any increase in incidence would have potentially immense clinical significance when multiplied across a potential patient population of many millions," the article said.

Patients taking taranabant also experienced gastrointestinal symptoms.

An advisory panel to the U.S. Food and Drug Administration in June recommended that rimonabant -- also known by its brand name Acomplia -- not be approved because it may increase suicidal thoughts and depression.

In a separate 24-hour food-intake study described in the Cell Metabolism article, a 12-milligram dose of taranabant cut calorie intake by about 20 percent, compared with placebo, while a related study showed a modest increase in energy expenditure. Merck said a considerably smaller dose is being tested in the ongoing Phase III trial.

"In doses we're studying, we believe the drug can be effective in weight loss, yet be safe," said Merck spokeswoman.

She cautioned that favorable weight-loss trends seen in the mid-stage studies must be confirmed by the larger Phase III trial and that safety must be explored further.

"There is so much hype about obesity and weight-loss treatments in general; we need to wait for reliable data," said Rose.

She noted that much of the data from the mid-stage taranabant studies was presented in October at a medical meeting in New Orleans.

Source: Diabetes In Control