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OREXIGEN THERAPEUTICS, INC. filed this Form S-1/A on 04/09/2007
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As a second benefit, both bupropion and naltrexone are known to act on the reward pathways in the brain that have been implicated in addiction to a number of substances, including food. These reward pathways are primarily regulated by dopamine and endogenous opioids, which are the targets of bupropion and naltrexone, respectively. Given that both drugs are approved for addiction-related disorders, we expect that together they may attenuate food craving and reward. As a result, we expect that Contrave may have an additional therapeutic benefit in patients who report food craving or obsession, which drives them to eat even when not hungry.
Contrave Clinical Results
Phase II Clinical Trial.  We initiated clinical testing of Contrave with a Phase II clinical trial in 2004. This trial enrolled 238 patients at eight U.S. clinical trial sites to evaluate the safety and efficacy of the Contrave combination. Patients accepted for the trial had a BMI in the range of 30 to 40, were non-smokers and did not have diabetes or other significant medical complications. On average, patients enrolled in this trial weighed approximately 95 kilograms, or 209 pounds, at the beginning of the trial, or baseline. Patients were randomly placed into one of four treatment groups:
  •      combination therapy, which consisted of 50mg naltrexone IR plus 300mg bupropion SR;
  •      bupropion monotherapy, which consisted of 300mg bupropion SR plus placebo;
  •      naltrexone monotherapy, which consisted of 50mg naltrexone IR plus placebo; and
  •      placebo, which consisted of two placebo pills.
The primary endpoint for this trial was percent change in body weight measured 16 weeks after the start of treatment, with secondary endpoints that included the percent change in body weight 24 weeks after the start of treatment, and response rates based on the percentage of patients who lost at least 5% and 10% of their baseline weight 16 and 24 weeks after the start of treatment. The outcomes for patients receiving the combination regimen were compared to each individual monotherapy and placebo. We also monitored the safety and tolerability of Contrave in this trial. The statistical analysis plans for the first Phase II clinical trials for Contrave and Empatic specified the use of an adjusted least-squares mean methodology for analysis of the primary endpoints. Accordingly, we have reported our results for these trials using this methodology. Least-squares mean methodology is based on a linear regression technique applied by statisticians to clinical trial data. We note that graphs that show weight loss over time for each treatment group in our trials utilize arithmetic mean data, because we believe this is the typical methodology used to present this type of chronological data.
On an intent-to-treat basis, which includes all randomized patients who recorded at least one post-baseline body weight measurement, Contrave demonstrated in this trial mean weight loss of 4.0% of baseline body weight at 16 weeks, compared to 3.6% for bupropion alone, 2.0% for naltrexone alone and 1.0% for placebo. One important observation in this trial was that the benefit of adding naltrexone became more apparent over time, as weight loss curves for the combination therapy group gradually diverged from the bupropion monotherapy group. Accordingly, by 24 weeks, Contrave showed 5.2% weight loss on an intent-to-treat basis, compared to 4.0% for bupropion alone. When this analysis is restricted to those patients who completed 16 weeks of treatment, Contrave demonstrated mean weight loss of 4.8% of baseline body weight, compared to 3.9 % for bupropion alone, 2.3% for naltrexone alone and 1.0% for placebo. By 24 weeks, Contrave showed 6.8% weight loss among completers, compared to 4.5% for bupropion alone.