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Merck obesity drug to continue at low dose

Published on 11/04/08 at 05:14pm

New data suggests Merck's taranabant drug can help obese patients lose weight, but safety concerns look to be behind higher doses of the drug being dropped.

Taranabant is in the same cannabinoid-1 receptor (CB1R) blocker class as Sanofi-Aventis' Acomplia, and Merck hope its drug can compete with Sanofi's product, which has been available in Europe since 2005.

Merck says the drug showed statistically significant weight loss when taken in combination with diet and exercise.

Obese patients taking taranabant 2mg experienced more than double the amount of weight loss at 52 weeks compared to placebo. Maximum weight loss was achieved by week 36 and was maintained throughout the next 16 weeks of the study, with patients demonstrating a mean reduction from baseline of 6.6 kg or 14.5 lbs (7.4 kg to 5.9 kg) compared to 2.6 kg or 5.7 lbs (3.3 kg to 1.8 kg) for patients on placebo.

The most common adverse events in the study were gastrointestinal and occurred more frequently in patients taking taranabant, but of most concern is the potential for psychological side-effects.

Acomplia has run into trouble because of its depression side-effects, and has been rejected for marketing approval by the US regulator over concerns about increased levels of depression in some patients taking the drug.

After studying data, European regulator the EMEA concluded in 2007 that the risk of depression is approximately doubled in patients taking Acomplia, compared to obese or overweight patients not taking the medicine.

Acomplia was nevertheless allowed to remain on the market but with strengthened contraindications and label warnings, and Merck will be hoping their drug doesn't display similar problems.

But the new data on taranabant suggests that greater incidences of psychiatric adverse events - such as tearfulness, mood swings, anxiety and depression - were seen in patients on the drug. This was particularly the case on high doses of the drug: on the 2mg dose 28% experienced them, while 40% had them on a 4mg dose and 38% on 6mg, compared with 20% on placebo.

Merck is pressing ahead with further phase III trials, but these fears about depression side-effects appear to have prompted the company to abandon the higher doses.

"Based on the benefit-risk considerations and the lack of a substantial improvement in the efficacy of taranabant at the 4mg and 6mg doses seen in our clinical programme compared to the 2mg dose, we have decided to continue to evaluate taranabant in doses up to and including 2mg in our phase III studies", said John Amatruda, vice president of clinical research, Metabolic Disorders, at Merck Research Laboratories. "We have a robust phase III clinical programme in place, and we look forward to presenting further results later this year".

In the UK, Acomplia was last month recommended for use on the NHS by NICE. But the recommendation is limited, with Acomplia only approved for patients who fail to respond to Roche's Xenical and Abbott's Reductil, are intolerant to them or for whom those drugs are contraindicated. Treatment should only continue after six months if the patient has lost at least 5% of their body weight.


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