While Merck and Pfizer pills targeting the same CB-1 receptor as rimonabant appear likely to be the next members of this class submitted for regulatory approval, UK company Vernalis on Sept. 13th reported its CB-1 receptor antagonist produced "striking weight loss" in two small phase I clinical trials.

The Vernalis drug, like the Merck, Pfizer and Sanofi drugs, works by suppressing a person's appetite. Vernalis said its drug produced weight-loss results that compared "very favorably" with results for rimonabant.

Average weight loss after 16 days was 1 pound for the overweight and mildly obese patients given a placebo, 6 pounds for those on a 5 mg dose of V24343 and 11 pounds for those on a 100 mg dose. 

But Vernalis said results for V24343 from its early trial showed "a markedly reduced propensity for neurological adverse events" and "a lower propensity to induce nausea and GI disturbance."

While Acomplia has been approved and is on sale in Europe, developer Sanofi-Aventis pulled back its application in the United States after it was unanimously thumbed down by an FDA advisory committee concerned over side-effects that included suicidal thoughts and behavior.

Vernalis said the concerns over "risks associated with depression, may be relevant to this class of drug.  However, the question as to whether or not other CB-1 antagonists can achieve similar or improved efficacy without major side effects remains open."

Pharmaceutical giants Merck with Taranabant and Pfizer are far ahead of Vernalis in exploring this, with drugs that target the CB-1 receptor already in large phase III trials.

Vernalis CEO Simon Sturge, nevertheless, said his company was "very excited by these preliminary results which, if confirmed over longer studies, will be of significant benefit to overweight and obese patients. 

"We stated from the outset of this trial that it is our intention to seek a partner for this program, a process which is enhanced by such promising data," he added.