11/15/2025
FDA Approves New Treatment for Thymidine Kinase 2 Deficiency
The U.S. Food and Drug Administration (FDA) has approved a new treatment for thymidine kinase 2 deficiency (TK2d) in adults and pediatric patients with an age of symptom onset on or before 12 years. Doxecitine and doxribtimine (Kygevvi) is a combination of doxecitine and doxribtimine, both pyrimidine nucleosides, administered as a powder for oral solution.
The safety and efficacy of doxecitine and doxribtimine (Kygevvi) were evaluated in a prospective, open-label, single-arm study in pediatric and adult patients with genetically confirmed TK2d previously treated with pyrimidine nucleosides (Trial 1). Additional safety information was derived from retrospective chart review studies (Study 1, Study 2) and from an expanded access program.
Warning and precautions for doxecitine and doxribtimine (Kygevvi) include elevated liver transaminase levels and gastrointestinal adverse reactions. The most common adverse reactions (≥5%) to doxecitine and doxribtimine (Kygevvi) are diarrhea, abdominal pain (including upper abdominal pain), vomiting, alanine aminotransferase increased (ALT), and aspartate aminotransferase increased (AST).
Healthcare professionals should report all serious adverse events suspected to be associated with the use of any medicine and device to the FDA’s MedWatch Reporting System or by calling 1-800-FDA-1088. Consumers are also encouraged to report adverse events to the FDA’s MedWatch site.
View the FDA’s announcement here:
https://www.fda.gov/drugs/novel-drug-approvals-fda/novel-drug-approvals-2025
View doxecitine and doxribtimine (Kygevvi) package insert here:
https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/219792s000lbl.pdf