The Food and Drug Administration’s Antimicrobial Drugs Advisory Committee backed the fixed dose combination of emtricitabine and tenofovir alafenamide (TAF; Descovy, Gilead) for pre-exposure prophylaxis (PrEP) against HIV for men and transgender women who have sex with men.
In a discussion after a 16-2 vote, committee members cited analysis by the study’s sponsor and the FDA showing efficacy and a generally good safety profile in the DISCOVER trial, the single new clinical trial conducted to support TAF’s use for pre-exposure prophylaxis (PrEP).
However, this trial included no cisgender women; the sponsor asked for approval based primarily on extrapolation from the DISCOVER results and previous results with tenofovir disoproxil fumarate (TDF) in cisgender women. Both formulations of tenofovir are prodrugs and converted to tenofovir diphosphate intracellularly in peripheral blood mononuclear cells, though many aspects of their pharmacokinetics differ.
The committee voted 10-8 against the proposition that these data supported an indication of TAF for PrEP in cisgender women, in a narrowly worded question from the FDA.
Many members who voted on either side of the question had strongly worded reservations about the lack of data for cisgender women. Said committee chair Lindsey R. Baden, MD, director of the infectious disease service at Dana-Farber Cancer Institute, Boston, who voted against the indication for cisgender women, “We’ve failed women. To be at this point and not have the data to guide decision-making is a shame on all of us.”
Ighovwerha Ofotokun, MD, who voted yes, concurred: “I agree it is a terrible failure that the agency, as well as the sponsor, would come to this committee with a lack of data on women.” But for Dr. Ofotokun, a professor of infectious diseases at Emory University, Atlanta, not including cisgender women in the approval was a distasteful proposition. “Creating a two-tier prevention and treatment hierarchy would not be helpful. We should remind ourselves that there are more women living with HIV in the world than there are men, and the risk of new HIV infection is higher among women than among men, if you look at this globally,” he said.
“I find it disrespectful and an issue of research equity. Women deserve the same quality of data about the safety and efficacy of the drugs they are exposed to that men get and that is not the situation we find ourselves in at the moment,” said Dawn K. Smith, MD, MPH, a lead scientist at the Centers for Disease Control and Prevention (CDC), Atlanta, who voted against approval for cisgender women.
Michael Green, MD, MPH, professor of pediatrics, surgery and clinical and translational science at the University of Pittsburgh, echoed the frustration of many committee members when he said, “I voted yes, almost abstained, then almost voted no.” He, along with all who voted yes, emphasized the importance of mandatory postmarketing studies in cisgender women to ensure efficacy data are obtained.
Transgender women made up only about 1% of the DISCOVER population, a fact that also gave many committee members pause.
If TAF is approved, labeling and package materials should be clear that the data support only noninferiority, not superiority, compared with TDF, said several advisory committee members who voted for approval for men and transgender women who have sex with men. “My expectation of this approval is that it should be marketed responsibly from the perspective of not creating these disparities and having Truvada be a drug for poor people and Descovy be a drug for rich people,” said Demetre Dasklalakis, MD, assistant commissioner of the Bureau of HIV/AIDS Prevention and Control at the city of New York’s Department of Health and Hygiene, and of the Icahn School of Medicine at Mount Sinai, N.Y. Truvada is slated to be offered as a generic drug in 2020, according to a Securities and Exchange Commission filing by Gilead Sciences.
The CDC reported earlier in 2019 that rates of new HIV infections have plateaued in recent years. Uptake of PrEP has been particularly low among at-risk members of minority populations, in rural areas, and in the South, according to a CDC report.
The DISCOVER trial is a 96-week ongoing trial to test TAF’s noninferiority to a fixed-drug combination of emcitrabine and tenofovir dimethyl fumarate (TDF; Truvada, Gilead) for PrEP. Both drugs are already approved to treat HIV infection, and TDF is approved for PrEP. Non-inferiority was preestablished at a rate ratio of HIV incidence of 1.62 (TAF:TDF) between the two study arms.
DISCOVER has enrolled 5,387 men and transgender women who have sex with men and are deemed at high risk for HIV, and found an incidence rate ratio of 0.47, with the upper bound of the confidence interval at 1.15. Since this figure was less than the prespecified noninferiority margin, both Gilead presenters and the FDA agreed, TAF’s noninferiority for efficacy was established.
Characteristics were similar between patients in the TAF arm (N = 2,694) and the TDF arm (N = 2,693). About 60% of patients in each arm reported having receptive anal sex with at least two partners in the previous 12 weeks, and recent rectal gonorrhea, syphilis, and chlamydia rates were 9-13% at baseline. Two thirds of participants reported recreational drug use, and about one in four reported binge drinking.
Sexual behavior and sexually transmitted infection rates continued generally unchanged from baseline during the study period.
The median age was 34 years, and most participants (84%) were white. Black participants made up 9% of the study population, and about 25% were of Hispanic or Latin ethnic origin.
Known decreases in bone mineral density occur with TDF; these were not seen with TAF, and bone mineral density increased while on TAF for the DISCOVER population aged 19-25 years.
Renal biomarkers of concern with TDF included two proteins linked with proximal tubule dysfunction, as well as estimated glomerular filtration rate. According to the sponsor’s analysis, eGFR fell by 2.3 mL/min for the TAF group, compared with a 1.8 mL/min rise while on TDF (P less than .001). Changes of similar statistical significance were seen for proximal tubular proteinuria. Also, improvements were seen in renal measures for the subset of patients enrolled who were on TDF PrEP at baseline but switched to TAF, in a prespecified subgroup analysis.
However, patients who were on TDF had a significant decrease in total cholesterol and both low- and high-density lipoprotein cholesterol compared with those on TAF, who had minimal changes or slight increases in lipids (P less than .001 for all). Triglycerides rose for those on TAF and remained unchanged for those on TDF (P = .002).
The PrEP indication sought by Gilead includes adults and adolescents, defined as those who weigh more than 35 kg. A nonvoting question put before the committee asked whether the totality of tenofovir data supported an indication of TAF for cisgender men who have insertive vaginal sex; though this extrapolation didn’t give the committee as much pause as the request for approval in cisgender women, they cited similar concerns and noted that cervicovaginal mucosa are different in many ways from rectal mucosa.
The study included no cisgender women, for a host of reasons cited by the sponsor and the FDA. These included high nonadherence rates among this population, relatively lower HIV infection rates among cisgender women in the United States, and mixed efficacy results in previous tenofovir clinical trials; the latter point made establishing a noninferiority margin problematic, according to the FDA.
For Dr. Baden, “The optics of approval for population A but not for population B are problematic.” Speaking to both the sponsor and the FDA, he said, “Everyone agrees there needs to be actual data. Please do the study as quickly as possible.” What’s needed is the collective will to make it happen, he added: “I don’t accept that it’s too big, too hard, too difficult.”
The FDA usually follows the recommendations of its advisory committees.
This article was updated 8/8/19.