FDA reviewer backs Gilead’s Descovy for PrEP, but not in women

Gilead Sciences’ Descovy, its successor to HIV pre-exposure prophylaxis (PrEP) therapy Truvada, is heading into an FDA advisory committee meeting on Wednesday with a mostly-positive verdict from the agency’s reviewer.

On the plus side, the briefing document published ahead of the meeting suggests that the clinical evidence puts Truvada and Descovy on a par when it comes to reducing HIV transmission in men and transgender women who have sex with men (MSM/TGW).

However, the reviewer notes that there isn’t much data available when it comes to cisgender women and adolescents, suggesting Gilead may struggle to get a label that covers the entire range of people who might benefit from Descovy for PrEP.

Gilead has argued that extrapolating the data from the DISCOVER trial that was filed in support of the application means that adolescents and women should be included.

The FDA reviewer agrees with the company when it comes to adolescents, but in the case of cisgender women says that pharmacokinetic data supposed to demonstrate Descovy reaches high enough concentrations in the vagina and cervix to provide protection is “compromised.”

That could be a big deal for Gilead, as it is trying to position Descovy (emtricitabine/tenofovir alafenamide) as a direct replacement for Truvada (emtricitabine/tenofovir disoproxil fumarate) with a more favourable side-effect profile – specifically on bone and kidney toxicity – before Truvada loses patent protection in 2021.

Truvada is currently the only FDA-approved drug for PrEP, meaning it can be given to individuals who are HIV-negative but at risk of being infected with HIV by a partner. It is estimated that two-thirds of Truvada’s $3 billion sales last year came from this use, and the threat of generic competition is why Gilead used a valuable priority review voucher (PRV) to speed up its FDA review time.

Gilead could already face a challenge convincing payers that Descovy’s more benign adverse event profile is worth the additional expense when Truvada generics appear on the market, although as PrEP is given to healthy individuals over a long period a cleaner safety profile could be a big asset.

However, its job could be made tougher if the new drug doesn’t have the same patient reach as its predecessor.

The reviewer is asking the advisory committee to discuss whether the DISCOVERY and other studies “allow for expansion of the Descovy PrEP indication to include cisgender women,” according to the briefing document.

It also wants the panel to tackle whether the data from the trial “are relevant to at‐risk men who practice insertive vaginal sex with cisgender women.”