After 12 months, there were no clinically significant differences in weight or metabolic changes between participants who switched from bictegravir/emtricitabine/tenofovir alafenamide (B/F/TAF) to long-acting injectable cabotegravir/rilpivirine (LAI CAB/RPV) and those who remained on B/F/TAF, according to research presented at the 30th Conference on Retroviruses and Opportunistic Infections (CROI 2023).
The SOLAR Study
Darrel H. S. Tan, M.D., Ph.D., of St. Michael's Hospital in Toronto, Canada, presented findings from the Phase 3b, multi-center, parallel-group SOLAR study. Participants—all of whom were virally suppressed on B/F/TAF for at least six months before study entry—were randomized 2:1 to remain on B/F/TAF or switch to LAI CAB/RPV. Those in the switch arm were given the option of starting with a one-month oral cabotegravir lead-in or changing immediately to injections. (Primary safety and efficacy data from the study were presented in a separate CROI 2023 presentation).
At study start, 227 participants remained on B/F/TAF, 175 participants elected the oral CAB lead-in (166 of whom switched to LAI CAB/RPV after one month) and 279 participants switched directly to LAI CAB/RPV. (After the 12-month primary endpoint, all participants were given the option to remain on, or switch to, LAI CAB/RPV during an extension phase.)
The study population included 12 transgender women, one transgender man and one gender non-conforming person. Demographic characteristics were similar between the arms: 17% to 18% of participants were female at birth, and about a fifth of participants in each arm were Black. At baseline, 59% of participants were overweight or obese, but few had diabetes or were taking lipid-lowering medications.
Reassuring Results
Over 12 months, participants in the B/F/TAF arm gained a median 0.05 kg and those in the LAI CAB/RPV arm lost a median 0.4 kg. For most people, this represented a modest change of less than 5% of their body weight, Tan said. Body weight changes of 10% or higher were observed in 4% (B/F/TAF) and 3% (LAI CAB/RPV) of participants, respectively.
While the body mass index (BMI) category changed little for most participants, a higher proportion of participants moved from normal weight to overweight in the B/F/TAF arm (7%) than in the LAI CAB/RPV arm (13%). That said, Tan noted that no participants moved from normal weight to obese in either arm, and the proportion of people who moved from overweight to obese was similar between the B/F/TAF arm (8%) and the LAI CAB/RPV arm (9%). There were no clinically relevant changes in waist and hip circumferences, although these measurements varied considerably among participants.
In response to a question from an audience member, Tan speculated that TAF-associated weight gain may have occurred among the participants before study entry. Participants had been on antiretroviral therapy for a median 2.5 years at baseline, and had been on B/F/TAF for at least 6 months based on the study inclusion criteria. Combined with the large proportion of obese/overweight participants, this suggests that weight had already increased before study start, Tan said.
More Analyses and Data to Come
Responding to comments and questions from audience members, Tan explained that several analyses had not been performed yet that would further explore the study results. For example, he said that in the future, data will be shared that stratify results by sex and race, which will hopefully help elucidate any differences in weight-related parameters in specific demographic groups (such as Black women) that have been observed in other research. That said, Tan noted that an initial look by the study investigators suggested that there was no such difference in the current study.
The Presentation
Abstract 146, “Weight and Metabolic Changes With Cabotegravir+Rilpivirine Long-Acting or Bictegravir,” presented by Darrel H. S. Tan, M.D., F.R.C.P.C., Ph.D., during the “Consternation About Complications” session of CROI 2023 on Feb. 21, 2023.