• Food and Drug Administration staff appear confident an HIV treatment developed by Gilead can also help prevent the disease from spreading, though the two parties are divided on whether it would have that effect for all women.
• Documents released ahead of a Wednesday advisory committee meeting show the staff believe a clinical trial called DISCOVER supports the use of Gilead’s Descovy as pre-exposure prophylaxis, or PrEP, for adult men and transgender women who have sex with men and are at risk of contracting HIV. Another Gilead product, Truvada, is the only drug to hold a PrEP indication.
• Gilead argues data from DISCOVER and past Truvada studies can be extrapolated to show how Descovy would also benefit adolescents and cisgender women at risk of getting HIV. FDA staff agreed with Gilead regarding adolescents but weren’t sold on cisgender women, noting how they may need more data showing that Descovy stays in high enough concentrations in vaginal tissue to prevent HIV exposure.

With its flagship hepatitis C business in free fall, Gilead has relied heavily on HIV drugs to prop up revenue. The California-based biotech controls about 75% of the HIV market, touting six blockbuster brands.

Truvada, a combination of the drugs emtricitabine and tenofovir disoproxil fumarate, is one such brand. It raked in $3 billion last year, making it the second biggest product by sales in Gilead’s portfolio.

Yet the key patent protecting Truvada from generic competition in the U.S. expires in 2021, putting pressure on Gilead to find a replacement. The company contends that it has an even better PrEP drug in Descovy, which also has the active ingredient emtricitabine, but pairs it with a newer antiretroviral drug called tenofovir alafenamide or TAF.

In March, Gilead presented results from the DISCOVER study that showed Descovy was non-inferior to Truvada when used for PrEP. Descovy also beat Truvada on secondary safety endpoints of bone and renal safety.

FDA staff seem to be on the same page as Gilead regarding Descovy’s use in PrEP. Where they differ, however, is in the applicable populations.

DISCOVER enrolled only adult men and transgender women who have sex with men and are at risk of HIV infection. Though the staff appear comfortable applying the results to younger patients within those respective groups, extrapolating them to cisgender women is a tougher sell.

“[B]ased on a review of the available literature, the FDA considers that local tissue drug concentrations at the site of potential HIV exposure are important to the prevention of HIV transmission,” the agency staff wrote.

“After review of the submitted data to support such an extrapolation approach, the FDA is uncertain that the data can support the efficacy of Descovy as PrEP in cisgender women.”

At the Wednesday advisory committee meeting, panelists will vote on two questions, with one being whether the data from DISCOVER and past Truvada trials offers enough evidence for a Descovy PrEP approval in cisgender women. If the panelist votes no, they’ll be asked to provide their rationale, including additional studies they’d like to see.

The Centers for Disease Control and Prevention estimates that 19% of the 38,739 new patients diagnosed with HIV in 2017 were women.

By the second quarter, around 213,000 HIV patients in the U.S. were on Truvada, according to Cantor Fitzgerald. The investment bank estimates that by 2025 Descovy sales will hit $1.5 billion collectively between prevention and non-prevention use.