Doxribtimine

Administration of KYGEVVI is intended to incorporate the pyrimidine nucleosides, deoxycytidine and deoxythymidine, into skeletal muscle mitochondrial deoxyribonucleic acid (DNA). This action restores mitochondrial DNA copy number in TK2d mutant mice.

• KYGEVVI is indicated for the treatment of thymidine kinase 2 deficiency (TK2d) in adults and pediatric patients with an age of symptom onset on or before 12 years. KYGEVVI is a combination of doxecitine and doxribtimine, both pyrimidine nucleosides, indicated for the treatment of thymidine kinase 2 deficiency (TK2d) in adults and pediatric patients with an age of symptom onset on or before 12 years.

• None. None.contraindicated

Obtain baseline transaminase (alanine aminotransferase [ALT] and aspartate aminotransferase [AST]) levels in all patients prior to treatment initiation. ( 2.1 ) Recommended dosage ( 2.2 ): KYGEVVI Dosage Level KYGEVVI Dosage (mg/kg/day) Starting 260 mg/kg/day (consisting of 130 mg doxecitine and 130 mg doxribtimine) Intermediate 520 mg/kg/day (consisting of 260 mg doxecitine and 260 mg doxribtimine) Maintenance 800 mg/kg/day (consisting of 400 mg doxecitine and 400 mg doxribtimine) Titrate to the next dosage level based on tolerability after a minimum of 2 weeks at the current dosage level. ( 2.2 ) Administer KYGEVVI orally in 3 equally divided doses with food. ( 2.2 ) See full prescribing information for dosage and administration modifications, monitoring, and preparation and administration instructions. ( 2.4 ) Use KYGEVVI only with ZX2000 administration kit. ( 2.4 ) 2.1 Important Recommendation Prior to KYGEVVI Treatment Initiation Obtain baseline liver transaminase (alanine aminotransferase [ALT] and aspartate aminotransferase [AST]) and total bilirubin levels in patients prior to treatment initiation with KYGEVVI [see Dosage and Administration (2.3) and Warnings and Precautions (5.1) ] . 2.2 Recommended Dosage The recommended dosage of KYGEVVI is based on the patient's weight (Table 1). Titrate to the next dosage level based on tolerability after a minimum of 2 weeks at the current dosage level.

Elevated Liver Transaminase Levels : Obtain baseline liver transaminase (ALT, AST) and total bilirubin levels prior to treatment initiation with KYGEVVI. If signs or symptoms consistent with liver injury are observed, interrupt treatment. Consider permanently discontinuing KYGEVVI if signs/symptoms consistent with liver injury persist or worsen. Monitor patients yearly and as clinically indicated. ( 5.1 ) Gastrointestinal Adverse Reactions : Reduce KYGEVVI dosage or interrupt treatment based on severity of diarrhea and/or vomiting. If persistent severe diarrhea and/or vomiting occurs, consider discontinuing KYGEVVI permanently. ( 5.2 ) 5.1 Elevated Liver Transaminase Levels Elevated liver transaminase [alanine aminotransferase (ALT) and/or aspartate aminotransferase (AST)] levels were reported in patients treated with KYGEVVI [see Adverse Reactions (6.1) ] . In Study 1, two patients permanently discontinued treatment with KYGEVVI upon recurrence of elevated liver enzymes after a rechallenge at a reduced dose. Obtain baseline liver transaminase (ALT, AST) and total bilirubin levels in patients prior to treatment initiation with KYGEVVI. If signs or symptoms consistent with liver injury are observed, interrupt treatment with KYGEVVI until liver transaminase (ALT, AST) and total bilirubin levels have either returned to baseline or stabilized at a new baseline value. Consider permanently discontinuing KYGEVVI if signs or symptoms consistent with liver injury persist or worsen.

The following clinically significant adverse reactions are described elsewhere in the labeling: Elevated Liver Transaminase Levels [see Warnings and Precautions (5.1) ] Gastrointestinal Adverse Reactions [see Warnings and Precautions (5.2) ] Most common adverse reactions (incidence ≥5%) are diarrhea, abdominal pain (including abdominal pain upper), vomiting, alanine aminotransferase increased (ALT), and aspartate aminotransferase increased (AST). ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact UCB, Inc. at 1-844-599-2273 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. The safety of KYGEVVI was 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 [see Clinical Studies (14) ] . Permanent discontinuation of KYGEVVI due to an adverse reaction occurred in 9% of patients (Trial 1, Study 1, and Study 2). The adverse reactions which resulted in permanent discontinuation of KYGEVVI in >2% of patients were diarrhea (3%) and elevated liver enzymes (3%).

8.1 Pregnancy Risk Summary There are no available data on KYGEVVI use during pregnancy to evaluate for a drug-associated risk of major birth defects, miscarriage, or other adverse maternal or fetal outcomes. Endogenous pyrimidine nucleosides are transported across the placenta. There are risks for adverse maternal and fetal outcomes during pregnancy with mitochondrial myopathies, including TK2 deficiency ( see Clinical Considerations ). In animal reproduction studies, oral administration of doxecitine and doxribtimine to pregnant rats and rabbits during organogenesis resulted in maternal and fetal toxicities in the rabbit at dose exposures 1233 and 811 times the maximum recommended human dose (MRHD) of 400 mg/kg/day doxecitine and 400 mg/kg/day doxribtimine, respectively, based on plasma exposure, but were not observed in the rat ( see Data ). The background risk of major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2% to 4% and 15% to 20% respectively.

Metabolism

Following oral administration of doxecitine and doxribtimine in healthy adult subjects, the baseline-adjusted maximum plasma concentration (C max ) and area under the plasma concentration-time curve (AUC) increased in a less than dose proportional manner for doxecitine at doses ranging from 43 mg/kg to 133 mg/kg and more than dose proportional manner for doxribtimine at doses ranging from 43 mg/kg to 133 mg/kg. There is minimal or no accumulation of doxecitine and doxribtimine following multiple dose administrations.

• Nov 3, 2025NDANDA219792Ucb Inc

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Recent PubMed references pinned to Doxribtimine as a MeSH major topic. Citations link to pubmed.ncbi.nlm.nih.gov.

• Feasibility Study of Trifluridine/Tipiracil and Zolbetuximab as Third- or Later-Line Chemotherapy for CLDN18.2-Positive and HER2-Negative Gastric or Gastroesophageal Junction Adenocarcinoma: A Study Protocol.
  Cancer medicine · 2026 · Maeda O, Tanaka C, Furukawa K, et al.
  PMID 42163549DOI 10.1002/cam4.71981
• FRUQUITAS trial: Study design of an ENGIC intergroup randomized phase III of trifluridine/tipiracil +/- fruquintinib in pre-treated metastatic gastro-oesophageal adenocarcinoma.
  Digestive and liver disease : official journal of the Italian Society of Gastroenterology and the Italian Association for the Study of the Liver · 2026 · Tougeron D, Rivera F, Kanonnikoff TF, et al.
  PMID 42108156DOI 10.1016/j.dld.2026.04.004
• Single-probe Pd-modified ZnO-polymer fluorescent sensor array for discrimination of thymidine analogues in aqueous media.
  Analytica chimica acta · 2026 · Gaur K, Ranbir, Kaur N, et al.
  PMID 42108062DOI 10.1016/j.aca.2026.345534
• Evaluation of optimal growth conditions for Enterobacterales thymidine-dependent small-colony variants: A pilot study for the development of antimicrobial susceptibility testing.
  Journal of microbiological methods · 2026 · Negishi T, Matsumoto T, Kamijo T, et al.
  PMID 42082114DOI 10.1016/j.mimet.2026.107530
• Fruquintinib Plus TAS-102 With or Without SBRT as Third- Or Later-Line Therapy for Metastatic Colorectal Cancer: Preliminary Results From a Prospective Phase II Trial.
  Cancer medicine · 2026 · Wang Y, Xu J, Liang L, et al.
  PMID 42057329DOI 10.1002/cam4.71884
• Synthesis and biophysical evaluation of C-5-triazolyl-functionalized morpholino-thymidine analogs.
  Organic & biomolecular chemistry · 2026 · Ghosh A, Acharya S, Kundu J, et al.
  PMID 42028662DOI 10.1039/d5ob01995h
• Predictive factors for early mortality after regorafenib or trifluridine/tipiracil initiation in metastatic colorectal cancer.
  The oncologist · 2026 · Masuishi T, Fukuoka S, Takashima A, et al.
  PMID 41992834DOI 10.1093/oncolo/oyag142
• Comparative evaluation of human T lymphocytes in HIV patients treated with lamivudine + zidovudine combined with nevirapine versus efavirenz.
  Medicine · 2026 · Zhu X, Zou M
  PMID 41961664DOI 10.1097/MD.0000000000048049

The 3 most recently updated of 3 ClinicalTrials.gov registrations naming Doxribtimine as an intervention. Registration is not evidence of efficacy or safety — reference crosswalk only.

• Doxecitine and Doxribtimine-Expanded Access
  Available · Expanded access · UCB BIOSCIENCES, Inc.
  NCT06590493updated 2026-06-05
• An Open-Label Study of Continuation Treatment With Combination Pyrimidine Nucleosides in Patients With TK2 Deficiency
  Active not recruiting · Phase 2 · Interventional · 47 enrolled · UCB BIOSCIENCES, Inc.
  NCT03845712updated 2026-05-01
• Doxecitin and Doxribthymine in Adult Subjects With Thymidine Kinase 2 (TK2) Deficiency
  Recruiting · Phase 2 · Interventional · 15 enrolled · Cristina Domínguez González
  NCT06754098updated 2025-07-28

Frequently asked questions

How does Doxribtimine work?

Administration of KYGEVVI is intended to incorporate the pyrimidine nucleosides, deoxycytidine and deoxythymidine, into skeletal muscle mitochondrial deoxyribonucleic acid (DNA). This action restores mitochondrial DNA copy number in TK2d mutant mice.

What is Doxribtimine used for?

According to FDA labeling, Doxribtimine carries indications including: KYGEVVI is indicated for the treatment of thymidine kinase 2 deficiency (TK2d) in adults and pediatric patients with an age of symptom onset on or before 12 years. KYGEVVI is a combination of doxecitine and doxribtimine, both pyrimidine nucleosides, indicated for the treatment of thymidine kinase 2 deficiency (TK2d) in adults and pediatric patients with an age of symptom onset on or before 12 years.. This is a reference summary of labeled uses, not medical advice or a treatment recommendation.

What are the brand names for Doxribtimine?

Doxribtimine is marketed under brand names including Kygevvi.

What are the contraindications for Doxribtimine?

Doxribtimine labeling lists contraindications including: None. None.. Always consult the full prescribing information and a clinician.