Pfizer's HIV Drug Gets FDA Nod

Selzentry is a CCR5 antagonist, also called a CCR5 inhibitor. These drugs block HIV from entering a pathway on the cell surface called the CCR5 coreceptor. CCR5 is one of two pathways for the virus; the drug doesn't guard against HIV entering cells through the other pathway.

The FDA endorsed Selzentry under its accelerated-approval program, called Subpart H, which allows a drug to be marketed without the traditional clinical-trial milestones. This program often is applied to cancer or HIV drugs in which a new drug appears to offer a "meaningful therapeutic advantage" over existing treatments for serious or life-threatening diseases.

The accelerated approval means there still could be setbacks for the drug.

Selzentry's approval was based on clinical trials of 24 weeks that showed that approximately twice as many patients taking Selzentry plus traditional therapy had undetectable levels of HIV compared with people on traditional therapy alone, Pfizer said.

"Longer-term data will be required before the FDA can consider traditional approval," Pfizer said. In this case, Pfizer must show that Selzentry reduces the level of virus after 48 weeks.

The drug's "traditional approval" prospects will be enhanced if the 48-week trials show patients have a higher level of CD4 cells, an important white blood cell that helps fight infection. After 24 weeks of testing, the Selzentry group had greater increases in CD4 cells than did the standard-therapy group.

If the 48-week tests fail to show similar safety and effectiveness for the Selzentry group vs. the traditional-care group, the FDA could order the drug removed from the market.