Health officials
repeated safety concerns about an experimental group of
HIV drugs Friday, days before government advisers will
recommend whether the first drug from the class merits
approval.
Pfizer seeks Food
and Drug Administration approval for maraviroc,
potentially the first in a novel group of drugs to fight
HIV, the virus that causes AIDS. Pfizer proposes
marketing maraviroc as Celsentri.
Pfizer believes
there is a clear unmet need for new drugs to fight HIV in
patients for whom other, older drugs no longer work.
Celsentri is unlike any other HIV medicines now on the
market in that it targets the cells of patients and
not the virus itself.
The FDA has
scheduled a Tuesday meeting of outside experts to discuss
Pfizer's application for approval. The FDA has asked the
experts whether Celsentri, if approved, would require
special labeling or if further study of the drug's
safety is needed before it can be sold. FDA also asked
whether the drug should be studied further in women and
blacks.
The FDA and
Pfizer both said that studies showed adding Celsentri to a
traditional HIV treatment regimen was more effective in
dropping the virus below detectable levels in
patients.
But the FDA
continues to be concerned about potential safety issues with
the entire class of drugs, called CCR5 receptor antagonists.
Those issues include the possibility the drugs could
increase the likelihood of infection, lymphoma, or
liver damage in HIV patients. They've also been linked
to heart rhythm changes in laboratory animals.
Most worrisome is
that the drugs could accelerate a shift from one
variant of HIV to a second, which is most often seen in the
sickest AIDS patients. Patients on Celsentri likely
would have to be tested regularly to monitor whether
the drug is driving such a shift.
Still, FDA
reviewers noted no increase in lymphomas or infections among
patients given Celsentri but said there was a modest
increase in liver problems.
Pfizer, in its
own analyses of studies of the drug, said the studies
showed no significant effect on the heart, and no increased
incidence of liver problems, cancer, or infection
compared with treatment with other HIV drugs.
Previously, those
sorts of safety concerns set back GlaxoSmithKline and
Schering-Plough in their development of similar CCR5
receptor antagonists.
The drugs block a
secondary but crucial doorway typically used by the
human immunodeficiency virus to enter white blood cells. A
body's white blood cells play an important role in the
immune system.
Researchers have
known for more than a decade that people who lack a
working version of that doorway, called a receptor, are at
best highly resistant to infection by HIV and at worst
slow to develop AIDS once infected.
Since 1987 the
FDA has approved 29 drugs, including combination
medicines, in four different classes to fight HIV. CCR5
receptor antagonists would represent a new fifth
class. (Andrew Bridges, AP)
