Kygevvi®
Doxecitine and doxribtimine (doxecitine/doxribtimine) is a fixed combination of 2 pyrimidine nucleosides.1
Doxecitine and doxribtimine has the following uses:
Doxecitine/doxribtimine 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.1
Doxecitine/doxribtimine is available in the following dosage form(s) and strength(s):
Powder for oral solution containing 2 g doxecitine and 2 g doxribtimine1
Dosage and Administration in Adults and Pediatric Patients
Obtain baseline transaminase (ALT and AST) levels in all patients prior to treatment initiation.1
Doxecitine/doxribtimine should be prepared and administered by adults only.1 Reconstitute commercially available powder prior to administration.1 Use the ZX2000 administration kit provided separately to prepare and administer the prescribed dose.1 Refer to the Instructions for Use for full preparation and administration information on use of doxecitine/doxribtimine with the ZX2000 administration kit.1 Household devices such as measuring cups or spoons are not adequate measuring devices.1
The recommended dosage of doxecitine/doxribtimine is based on the patient's weight (see Table 1).1 Administer doxecitine/doxribtimine orally in 3 equally divided doses with food.1 Titrate to the next dosage level based on tolerability after a minimum of 2 weeks at the current dosage level.1
Dosage Level | 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) |
See full prescribing information for dosage modification recommendations for adverse effects, patient monitoring recommendations, and additional preparation and administration instructions.1
None.1
Elevated Liver Transaminase Levels
Elevated liver transaminase [alanine aminotransferase (ALT) and/or aspartate aminotransferase (AST)] levels were reported in patients treated with doxecitine/doxribtimine.1 In clinical studies, two patients permanently discontinued treatment with doxecitine/doxribtimine upon recurrence of elevated liver enzymes after a rechallenge at a reduced dose.1
Obtain baseline liver transaminase (ALT, AST) and total bilirubin levels prior to treatment initiation with doxecitine/doxribtimine.1 If signs or symptoms consistent with liver injury are observed, interrupt treatment until liver transaminase (ALT, AST) and total bilirubin levels have either returned to baseline or stabilized at a new baseline value.1 Consider permanently discontinuing doxecitine/doxribtimine if signs or symptoms consistent with liver injury persist or worsen.1 Monitor liver transaminases and total bilirubin levels yearly and as clinically indicated.1
Gastrointestinal Adverse Reactions
Diarrhea and vomiting leading to hospitalization, dose reduction, and permanent discontinuation were reported in patients treated with doxecitine/doxribtimine.1 Based on severity, reduce the dosage of doxecitine/doxribtimine or interrupt treatment until diarrhea and/or vomiting improves or returns to baseline.1 Consider restarting doxecitine/doxribtimine at the last tolerated dose, and increase the dose as tolerated.1 For persistent or recurring diarrhea and/or vomiting, consider discontinuing doxecitine/doxribtimine permanently and provide supportive care with electrolyte repletion as clinically indicated.1
There are no available data on doxecitine/doxribtimine use during pregnancy to evaluate for a drug-associated risk of major birth defects, miscarriage, or other adverse maternal or fetal outcomes.1 Endogenous pyrimidine nucleosides are transported across the placenta.1 There are risks for adverse maternal and fetal outcomes during pregnancy with mitochondrial myopathies, including TK2 deficiency.1 In animal reproduction studies, oral administration of doxecitine/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.1
The background risk of major birth defects and miscarriage for the indicated population is unknown.1 All pregnancies have a background risk of birth defect, loss, or other adverse outcomes.1 In the U.S.1 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.1
Mitochondrial myopathies are associated with increased adverse perinatal outcomes, including preterm birth, pre-eclampsia and gestational diabetes.1
There are no data on the presence of doxecitine and doxribtimine or its metabolites in either human or animal milk, the effects on the breastfed infant, or the effects on milk production.1 Data from published literature report the presence of nucleosides and nucleotides in human milk.1 The developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for doxecitine/doxribtimine and any potential adverse effects on the breastfed infant from the combination drug or from the underlying maternal condition.1
Females and Males of Reproductive Potential
Doxecitine and doxribtimine had no effect on male or female fertility or early embryonic development at doses up to 2000 mg/kg/day in rats (1131 times and 1223 times the MRHD in males and females respectively for 400 mg/kg/day doxecitine and 1056 times and 425 times the MRHD in males and females respectively for 400 mg/kg/day doxribtimine, based on plasma exposure).1
The safety and effectiveness of doxecitine/doxribtimine for the treatment of thymidine kinase 2 deficiency (TK2d) have been established in pediatric patients with an age of symptom onset on or before 12 years.1 Use of doxecitine/doxribtimine for this indication in this population is supported by evidence from two retrospective studies (Study 1, Study 2), one open-label study (Trial 1), and an expanded access program in which a total of 68 patients 0.7 years of age to less than 17 years of age were treated.1 In Trial 1, compared to adults, a higher percentage of pediatric patients experienced adverse reactions of vomiting and elevated liver transaminases.1 Serious adverse reactions in the pediatric population included hospitalization due to diarrhea in two patients.1
Clinical studies of doxecitine/doxribtimine did not include sufficient number of patients 65 years of age and older to determine whether they respond differently from younger adult patients.1
No studies have been conducted to evaluate the effect of hepatic impairment on the pharmacokinetics of doxecitine and doxribtimine.1
Plasma concentrations of doxecitine and doxribtimine increased in patients with moderate or severe renal impairment.1 The pharmacokinetics (PK) of doxecitine and doxribtimine have not been evaluated in patients with mild renal impairment.1 An appropriate dosage adjustment of doxecitine/doxribtimine in patients with renal impairment could not be determined because renal impairment had distinct effects on the PK of doxecitine and PK of doxribtimine, and it is not feasible to separately adjust the dosage for doxecitine or doxribtimine contained in the fixed combination preparation.1
Most common adverse reactions (incidence ≥5%) are diarrhea, abdominal pain (including abdominal pain upper), vomiting, alanine aminotransferase increased (ALT), and aspartate aminotransferase increased (AST).1
It is essential that the manufacturer's labeling be consulted for more detailed information on interactions with this drug, including possible dosage adjustments. Interaction highlights:
Please see product labeling for drug interaction information.1
Administration of doxecitine/doxribtimine is intended to incorporate the pyrimidine nucleosides, deoxycytidine and deoxythymidine, into skeletal muscle mitochondrial deoxyribonucleic acid (DNA).1 This action restores mitochondrial DNA copy number in thymidine kinase 2 deficiency (TK2d) mutant mice.1
Additional Information
AHFSfirstRelease™. For additional information until a more detailed monograph is developed and published, the manufacturer's labeling should be consulted. It is essential that the manufacturer's labeling be consulted for more detailed information on usual uses, dosage and administration, cautions, precautions, contraindications, potential drug interactions, laboratory test interferences, and acute toxicity.
Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.
Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.
Routes | Dosage Forms | Strengths | Brand Names | Manufacturer |
|---|---|---|---|---|
Oral | Powder for Oral Solution | 2 g doxecitine and 2 g doxribtimine per packet | Kygevvi | UCB |
AHFS® Drug Information. © Copyright, 1959-2025, Selected Revisions December 10, 2025. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, MD 20814.