Background: Definitions of virological failure and treatment discontinuation for long-acting injectable (LAI) cabotegravir and rilpivirine antiretroviral therapy are inconsistent in clinical practice and observational studies, which complicates interpretation and implementation of findings. The CONSENSUS-LAI study aimed to establish consistent definitions of virological failure and treatment discontinuation to enhance evidence transferability and support optimal clinical outcomes.

Methods: The study had two phases. Phase 1 was an international online survey exploring existing definitions of virological and treatment discontinuation, conducted between April 25 and July 1, 2024. Eligible participants were health-care professionals working in infectious disease or sexual health services who had provided care to at least ten people living with HIV in the past 6 months, had prescribed LAI cabotegravir and rilpivirine in clinical trials or clinical practice, and were able to give informed consent. Participants were recruited via social media and mailing lists of medical specialist societies. Phase 2 was a Delphi process, in which a panel of experts, selected to ensure representation from all six WHO regions, scored leading definitions from phase 1 on a 9-point Likert scale. The proposed definitions were scored according to four validity criteria: clarity, usability in the expert's setting, appropriateness across clinical purposes, and applicability across relevant population groups. Revisions were suggested in iterative rounds until consensus was reached. Consensus was predefined as at least 75% of experts agreeing or strongly agreeing (scores 7-9) with the validity criteria.

Findings: 386 LAI cabotegravir and rilpivirine prescribers across 28 countries completed the survey, revealing 15 definitions for virological failure on LAI cabotegravir and rilpivirine and nine for treatment discontinuation. 52 experts participated in the Delphi process. Consensus agreement on both definitions was reached after two rounds for all validity criteria. For virological failure, the consensus definition was as follows: (a) viral load 200 copies or more per mL or more on two occasions 2-4 weeks apart, or (b) a single viral load of more than 1000 copies per mL, and/or (c) emergent resistance, in the context of timely injections and prior suppression of less than 200 copies per mL, OR (d) unable to suppress viral load to less than 200 copies per mL on continuous therapy. For treatment discontinuation the consensus definition was as follows: people on LAI cabotegravir and rilpivirine who have missed two consecutive injections and have not taken oral bridging in the interim, irrespective of reason for discontinuation.

Interpretation: The consensus definitions provide a foundation for aligning practice and evaluating patient outcomes. Further validation of the viral load threshold for virological failure and the optimal viral load retesting window is required.

Funding: ViiV Healthcare.