Merck diet drug taranabant, which targets the same CB-1 receptor as Sanofi's obesity treatment Acomplia (rimonabant), also produces psychiatric side effects but results in almost-as-good weight loss at one-tenth the dosage, according to study results presented to the American College of Cardiology.
Merck said one-year results from a two-year Phase III trial showed that patients taking a 2 mg dose of taranabant had a mean weight loss reduction of 14.5 pounds compared to 5.7 pounds for patients on a placebo.
The researchers said 57 percent of the patients taking the 2 mg dose of taranabant lost five percent of their body weight, and 28 percent lost 10 percent of their body weight.
In contrast, Sanofi in Nov. 2004 reported that in its Phase III trial, 62.5 percent of patients taking the 20 mg dose of Acomplia lost more than 5 percent of their body weight, and 32 percent lost more than 10 percent of their body weigh.
But Sanofi also tested a 5 mg dose of Acomplia -- which has never been brought to market -- and said only 36.7 percent of those on the low dose lost more than 5 percent of their body weight, and only 20 percent lost 10 percent of their bodyweight.
While Merck also tested 4 mg and 6 mg doses of taranabant, it said the incidence of psychiatric side effects -- the problem that has thus far blocked approval of rimonabant for sale in the U.S. -- was greater at the higher doses, and that further development of taranabant would focus on the 2 mg dose.
The big question, of course, is whether the incidence and severity of psychiatric side effects -- which has kept Acomplia / Zimulti off the U.S. market -- is better for a 2 mg dose of taranabant than for a 20 mg dose of rimonabant.
It thus far has been hard to draw any meaningful comparisons between the psychiatric side effects noted for Acomplia and taranabant, in part because the measurement and recording of these appears to have been considerably enhanced in anticipation of a more rigorous FDA approval process.
Researchers reported that the incidence of psychiatric adverse events was 28 percent for patients on taranabant 2 mg, 40 percent on taranabant 4 mg, and 38 percent on taranabant 6 mg. How severe these may have been is not known.
But Merck made it clear today that as it continues efforts to get taranabant to a point where it can be submitted for FDA approval later this year, it intends to focus on development of a drug that produces significant weight loss at the lowest dosage possible.
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