Pfizer is seeking approval for maraviroc in patients already taking other drugs. If approved, it will be the first drug available in the class called CCR5 antagonists.
CCR5 antagonists stop the HIV virus from getting into cells by blocking the main entry point common to most people who have the infection. As resistance is a major problem in HIV treatment, new drug classes are needed to fight the disease.
However, CCR5 antagonists have raised safety concerns in the past. Earlier drugs under development were linked to lymphoma and liver damage. These risks did not appear to be significant in the Pfizer studies, but according to media reports, the FDA reviewers are concerned about modest increases in liver damage.