Injection Beats Pill for Long-Lasting HIV Prevention

Heather Boerner

July 09, 2020

Injections of cabotegravir (ViiV Healthcare) given every other month are more effective in blocking HIV transmission than the once-a-day combination of tenofovir disoproxil fumarate and emtricitabine (Truvada, Gilead Science), new data from the HPTN 083 trial show.

The findings "could transform the HIV prevention landscape for so many people," said Megan Coleman, DNP, from Whitman-Walker Health in Washington, DC, who regularly prescribes Truvada as pre-exposure prophylaxis (PrEP).

At Whitman-Walker alone, about 3000 people were taking the pill in early 2020, but "for some people, taking a pill every day just isn't a viable option," said Coleman. "To have something that can support a patient's choice and a patient's ability to reduce their own risk of HIV is amazing."

Final results from the trial — which looked at the drug in cisgender men and transgender women who have sex with men — were presented at the International AIDS Conference 2020.

Early Study Termination

Half of the 4566 study participants — from 43 sites in Africa, Asia, Latin America, and the United States — were younger than 30 years, 12.4% were transgender women, 29.7% were black, and 46.1% were Hispanic.

By design, ViiV Healthcare, the study sponsor, required that 50% of American participants be black to reflect the population at risk for HIV in the United States, said Raphael Landovitz, MD, from the UCLA David Geffen School of Medicine in Los Angeles, who is protocol chair for HPTN 083. In fact, 49.7% of the American cohort was black and 17.8% was Hispanic.

Patients randomized to the cabotegravir group received daily oral cabotegravir plus daily oral placebo for 5 weeks, to assess safety, followed by a cabotegravir injection at weeks 5 and 9 and every 2 months thereafter out to week 153 plus daily oral placebo. Patients randomized to the Truvada group received daily oral Truvada plus daily oral placebo for 5 weeks, followed by daily oral Truvada plus placebo injection, on the same schedule, out to week 153.

After the final injection, all participants continued on daily oral Truvada for 48 weeks.

The researchers expected to wait until 172 participants acquired HIV; they decided at the outset that this number would be sufficient to power a decision on whether or not cabotegravir injections are better than daily oral Truvada. But by May 2020, when 52 of the study participants had acquired HIV, the results were so lopsided in favor of cabotegravir that the trial was stopped. At that point, all participants were offered cabotegravir injections every 2 months.

Thirty-nine of the 52 (75%) new HIV infections occurred in the Truvada group. In fact, people in the cabotegravir group were less likely to acquire HIV than those in the Truvada group (hazard ratio, 0.34).

"This definitively establishes the superiority of cabotegravir," said Landovitz.

He and his colleagues had been legitimately concerned that HIV acquisition would be so low in the trial that they wouldn't be able to show how effective the injectable was. The success of Truvada PrEP has made it difficult to design prevention trials.

"We know that Truvada works extremely well, so the fact that we were able to show that cabotegravir in this population works better" is a powerful observation, said Landovitz. This is especially true because the rates of sexually transmitted infections — which are thought to increase risk for HIV transmission — were so high. Overall, 16.5% of the participants tested positive for syphilis during the trial, 13.3% tested positive for gonorrhea, and 21.1% tested positive for Chlamydia.

Five Surprising Seroconversions

Eleven of the 15 HIV infections in the cabotegravir group occurred in people who had received at least one injection. Three of these infections actually occurred during the first 5 weeks of the study when participants were taking oral cabotegravir, two occurred when participants chose to discontinue the injection and return to daily oral Truvada, and one occurred after a participant missed the injection for a prolonged period of time.

But five of the transmissions occurred in participants who appeared to be perfectly adherent.

Landovitz offered a number of possible reasons for this surprising finding.

"Number one could be that there's something about these five particular individuals such that they grind up and eliminate the cabotegravir faster than other people, so an 8-week interval is too long for them," he explained. "Another possibility, although pretty rare, is that there is a rare circulating virus that is intrinsically resistant to cabotegravir."

Breakthrough HIV transmissions have been rare in people taking oral PrEP.

Disruptions caused by the COVID-19 pandemic have meant that the researchers don't yet have the data on drug-resistant mutations or drug levels for these five participants, but they will.

"I suspect the truth is that there will never be a 100% failsafe HIV prevention mechanism," said Landovitz.

"Impressive" Findings

The findings were greeted with excitement, although questions remain.

They are "impressive," especially the data on black and Hispanic participants, said Paul Sax, MD, medical director of the Division of Infectious Diseases at Brigham and Women's Hospital in Boston.

However, he said he is interested in the data showing that although participants in both groups gained weight during the study, there was early weight loss in the Truvada group, meaning that those in the cabotegravir group weighed more at the end of the study than those in the Truvada group.

"I've been watching the data on weight with integrase inhibitors," he explained, including weight data specific to Truvada and to the combination of emtricitabine and tenofovir alafenamide (Descovy, Gilead). It looks like Truvada "has some sort of weight-suppressive effects. That's going to be a thing we're going to have to watch."

Coleman said she is already thinking about patients at Whitman-Walker who might do well on cabotegravir and those who can start PrEP for the first time with this option.

"Not only would people probably switch to this option, but maybe people would be interested in starting a biomedical prevention approach that isn't a pill every day," she said. "It's just exciting to have another option. Hopefully, in a few years, we'll have implantable devices and rings; I can't even imagine what all those brilliant minds are coming up with."

But that's still a ways off. First, cabotegravir has yet to be approved for HIV prevention, and ideally, eventually, there will be a way to determine if cabotegravir is safe for each patient that doesn't involve a month of daily pills.

"We need to solve that problem because it's so complicated to do an oral lead-in for a month or so," said Carl Dieffenbach, PhD, director of the Division of AIDS at the National Institute of Allergy and Infectious Diseases, National Institutes of Health. "Otherwise it's not going to be feasible."

We need to make sure this gets licensed for men and women and transgender individuals.

Even with these positive data, Dieffenbach and other officials are not keen to have ViiV apply for licensing right away. Last October, Descovy was the second oral PrEP pill approved for HIV prevention, but only for use by gay men and transgender women — it hadn't been well studied in cisgender women — causing an outcry. Now, officials are suggesting that ViiV not make the same mistake.

They are urging the company to hold off until data from the sister study of the medication in women — HPTN 084 — is completed in 2022.

"We need to make sure this gets licensed for men and women and transgender individuals," Dieffenbach told Medscape Medical News. "We just need to give this a little more time and then build a plan with contingencies, so that if something happens, we still have collected all the safety data in women so we can say it's safe."

ViiV seems to be making such a plan.

"Our goal is to seek approval across all genders and we will work with the FDA and other regulatory agencies to map out a plan to achieve this goal," said Kimberly Smith, MD, head of research and development at ViiV Healthcare.

The World Health Organization (WHO), meanwhile, doesn't expect to change its guidelines on HIV prevention medications until data from HPTN 084 are reported.

"What's important when we look at guidelines is that we also look across populations," said Meg Doherty, coordinator of treatment and care in the Department of HIV/AIDS at WHO. "We're waiting to know more about how cabotegravir works in women, because we certainly want to have prevention drugs that can be used in men and women at different age ranges and, ideally, during pregnancy."

International AIDS Conference 2020: Abstracts OAXLB01. Presented July 8, 2020.

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