The most common side effects include diarrhea, vomiting, increase in liver enzymes, and abdominal pain.[2]
Doxecitine/doxribtimine was approved for medical use in the United States in November 2025.[2]
Medical uses
Doxecitine/doxribtimine is indicated for the treatment of thymidine kinase 2 deficiency in people with an age of symptom onset on or before twelve years of age.[1][2]
Thymidine kinase 2 deficiency is a rare, inherited genetic disorder that affects the body's ability to produce and repair mitochondrial DNA.[2] Conditions that cause low levels of mitochondrial DNA, including thymidine kinase 2 deficiency, can be called mitochondrial depletion syndromes.[2] Symptoms of thymidine kinase 2 deficiency can include muscle weakness and respiratory (breathing) failure.[2] While the exact frequency of thymidine kinase 2 deficiency is not known, it is considered very rare.[2] Approximately 120 people have been described in the medical literature, although the condition may be underdiagnosed.[2]
Side effects
The most common side effects include diarrhea, vomiting, increase in liver enzymes, and abdominal pain.[2]
Mechanism of action
Doxecitine (deoxycytidine) and doxribtimine (deoxythymidine) are used as deoxynucleoside therapies to treat thymidine kinase 2 (TK2) deficiency, a mitochondrial DNA depletion syndrome caused by mutations in the nuclear TK2 gene. These compounds act by supplying exogenous deoxycytidine (dC) and deoxythymidine (dT) respectively, facilitating mitochondrial DNA replication through alternative cytosolic enzymes such as thymidine kinase 1 (TK1) and deoxycytidine kinase (dCK). The therapy thus bypasses the dysfunctional mitochondrial TK2 enzyme, allowing restoration or preservation of mtDNA synthesis and cellular energy metabolism in patients with TK2 deficiency.[3]
History
The efficacy of doxecitine/doxribtimine to treat people with thymidine kinase 2 deficiency who start to show symptoms when they are twelve years of age or younger was established based on data from one phase II clinical study, two retrospective chart review studies, and an expanded access program.[2] The survival in participants treated with doxecitine/doxribtimine was compared with the survival in an untreated external control group composed of untreated participants from published literature and one of the retrospective studies in this drug development program.[2]
Society and culture
Legal status
Doxecitine/doxribtimine was approved for medical use in the United States in November 2025.[4]
↑ Chow E, Miller L, Clearman A, Arnold P, Koenig MK, Russo SN (August 2025). "Doxecitine and doxribtimine treatment in an adult patient with thymidine kinase 2 deficiency". Molecular Genetics and Metabolism. 145 (4) 109159. doi:10.1016/j.ymgme.2025.109159. PMID40516470.
↑ World Health Organization (2022). "International nonproprietary names for pharmaceutical substances (INN): recommended INN: list 87". WHO Drug Information. 36 (1). hdl:10665/352794.
External links
Clinical trial number NCT03845712 for "An Open-Label Study of Continuation Treatment With Combination Pyrimidine Nucleosides in Patients With TK2 Deficiency (Continuation)" at ClinicalTrials.gov
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