Translational progress and bottlenecks in kappa-opioid receptor agonist analgesia research (1990–2026): an integrated bibliometric and clinical trial registry analysis

Scoping review combining three linked layers. (1) Bibliometric layer: the published literature on kappa-opioid receptor (KOR) agonist analgesia, 1990-2026, indexed in the Web of Science Core Collection, analysed for temporal trend, collaboration structure, knowledge base and translational stage. (2) Trial registry layer: registered interventional trials of KOR agonists retrieved from ClinicalTrials.gov, the WHO ICTRP, the China CDE platform and ChiCTR, analysed for number, phase, indication, geography, sponsorship and completeness of results reporting. (3) Bridging layer: completed analgesic trials linked to their publications, to estimate the publication rate, the completion-to-publication interval and the concordance of registered and published primary outcomes. No effect estimates are pooled and no health-related outcome is estimated. The review is registered retrospectively: all searches, extraction and analyses were completed before registration, and the protocol was not modified thereafter.