Efficacy, safety, and tolerability of switching to long-acting cabotegravir plus rilpivirine versus continuing fixed-dose bictegravir, emtricitabine, and tenofovir alafenamide in virologically suppressed adults with HIV, 12-month results (SOLAR): a randomised, open-label, phase 3b, non-inferiority trial

Background: Cabotegravir plus rilpivirine is the only approved complete long-acting regimen for the maintenance of HIV-1 virological suppression dosed every 2 months. The SOLAR study aimed to compare long-acting cabotegravir plus rilpivirine every 2 months with continued once-daily bictegravir, emtricitabine, and tenofovir alafenamide for the maintenance of HIV-1 virological suppression in adults living with HIV.

Methods: SOLAR is a randomised, open-label, multicentre, phase 3b, non-inferiority study. The study was done in 118 centres across 14 countries. Participants with HIV-1 RNA less than 50 copies per mL were randomly assigned (2:1), stratified by sex at birth and BMI, to either long-acting cabotegravir (600 mg) plus rilpivirine (900 mg) dosed intramuscularly every 2 months or to continue daily oral bictegravir (50 mg), emtricitabine (200 mg), and tenofovir alafenamide (25 mg). Participants randomly assigned to long-acting therapy had a choice to receive cabotegravir (30 mg) plus rilpivirine (25 mg) once daily as an optional oral lead-in for approximately 1 month. The primary efficacy endpoint was the proportion of participants with virological non-response (HIV-1 RNA ≥50 copies per mL; the US Food and Drug Administration snapshot algorithm, 4% non-inferiority margin; modified intention-to-treat exposed population) at month 11 (long-acting start with injections group) and month 12 (long-acting with oral lead-in group and bictegravir, emtricitabine, and tenofovir alafenamide group). The study is registered with ClinicalTrials.gov, NCT04542070, and is ongoing.

Findings: 837 participants were screened between Nov 9, 2020, and May 31, 2021, and 687 were randomly assigned to switch treatment or continue existing treatment. Of 670 participants (modified intention-to-treat exposed population), 447 (67%) switched to long-acting therapy (274 [61%] of 447 start with injections; 173 [39%] of 447 with oral lead-in) and 223 (33%) continued bictegravir, emtricitabine, and tenofovir alafenamide. Baseline characteristics were similar; median age was 37 years (range 18-74), 118 (18%) of 670 were female sex at birth, 207 (31%) of 670 were non-White, and median BMI was 25·9 kg/m² (IQR 23·3-29·5). At month 11-12, long-acting cabotegravir plus rilpivirine showed non-inferior efficacy versus bictegravir, emtricitabine, and tenofovir alafenamide (HIV-1 RNA ≥50 copies per mL, five [1%] of 447 vs one [<1%] of 223), with an adjusted treatment difference of 0·7 (95% CI -0·7 to 2·0). Excluding injection site reactions, adverse events and serious adverse events were similar between groups. No treatment-related deaths occurred. More long-acting group participants had adverse events leading to withdrawal (25 [6%] of 454 vs two [1%] of 227). Injection site reactions were reported by 316 (70%) of 454 long-acting participants; most (98%) were grade 1 or 2.

Interpretation: These data support the use of long-acting cabotegravir plus rilpivirine dosed every 2 months as a complete antiretroviral regimen that has similar efficacy to a commonly used integrase strand transfer inhibitor-based first-line regimen, while addressing unmet psychosocial issues associated with daily oral treatment.

Funding: ViiV Healthcare.