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Pfizer Inc., the world’s largest drugmaker, on Wednesday
said it abandoned an obesity drug known only by the designation CP-945,598 –
not specifically for safety concerns but because of “changing regulatory
perspectives on the risk/benefit profile of the CB1 class and likely new
regulatory requirements for approval.”
“While confident in the safety of the compound, we believe that this is the
appropriate decision based on all available information regarding this class of
agents, as well as recent discussions with regulatory authorities,” Martin
Mackay, president of Pfizer Global Research and Development, said in a
statement.
The drug was in the third of three stages of testing required for market
clearance and could have more than $500 million in annual sales, according to
analysts.
The drug works by blocking the same brain receptor that makes marijuana
smokers hungry, a process the FDA considers dangerous, as it could increase the
risk for other health conditions including mood disorders and neurodegenerative
disorders such as multiple sclerosis.
Pfizer’s announcement comes a months after Merck & Co.
announced its decision to cancel further investigation into its experimental
obesity drug called taranabant because of side effects uncovered in clinical
trials.
The company
said that both effectiveness and side effects were dependent on dose levels; at
more effective dosages, the side effects climb too much. The side effects
associated with the drug taranabant were psychiatric, including anxiety and
depression.
Taranabant
is also a cannabinoid-1 (CB-1) receptor inverse agonist, which means it works by
blocking cannabinoid receptors in the brain and it suppresses appetite.
Cannabinoid receptors are the same receptors that make people hungry when
smoking marijuana.
In 2007,
Sanofi-Aventis’ anti-obesity drug, generically known as rimonabant (Acomplia)
was also rejected by the Food and Drug Administration in the United States due
to concerns about the risk of suicidal thoughts and depression among some
users. According to a series of studies, not only does the obesity drug
increase the risk of depressed mood disorders and anxiety, but it is also
almost ineffective against obesity, as people lose less than 5 percent of their
total body weight.
At the end
of October, the European Medicines Agency announced that the risk of serious
psychiatric disorders and even suicide are too high in patients taking Acomplia.
The European Medicines Agency recommended pulling the drug from the market
because of its side effects.
The agency
had concluded that “the benefits of Acomplia no longer outweigh its risk” and
there was an approximate doubling of the risk of psychiatric disorders in obese
or overweight patients taking Acomplia versus a placebo. Data from recent
studies has shown the side effects were even higher. Between June and August
2008 there were five suicides among participants in the trial who took the
drug, compared to one among those taking a placebo.
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