Doxecitine and Doxribtimine: First Approval

DeclarationsAuthorship and Conflict of interest During the peer review process, the manufacturer of the agent under review was offered an opportunity to comment on the article. Changes resulting from any comments received were made by the authors on the basis of scientific completeness and accuracy. Hannah A. Blair is a salaried employee of Adis International Ltd/Springer Nature and declares no relevant conflicts of interest. All authors contributed to this article and are responsible for its content.Ethics approval, Consent to participate, Consent to publish, Availability of data and material, Code availability Not applicable.Additional information about this Adis Drug Review can be found here.Doxecitine and doxribtimine (KYGEVVI®) are pyrimidine nucleosides being developed by UCB for the treatment of thymidine kinase 2 deficiency (TK2d). In November 2025, doxecitine and doxribtimine received its first approval in the USA for the treatment of TK2d in adult and pediatric patients with an age of symptom onset on or before 12 years. This article summarizes the milestones in the development of doxecitine and doxribtimine leading to this first approval for TK2d.© The Author(s), under exclusive licence to Springer Nature Switzerland AG 2026