Thymidine Kinase 2 DeficiencyPhase 2ContinuationNCT03845712
An Open-Label Study of Continuation Treatment With Combination Pyrimidine Nucleosides in Patients With TK2 Deficiency
A Phase 2 study testing doxecitine and doxribtimine in people with Thymidine Kinase 2 Deficiency, run by UCB BIOSCIENCES, Inc. at 8 sites in 3 countries.
Trial summary
This is a Phase 2 prospective open-label treatment study of the safety and efficacy of doxecitine and doxribtimine in study participants with thymidine kinase 2 (TK2) deficiency who participated in the retrospective study MT-1621-101 [NCT03701568] or who were receiving nucleos(t)ide treatment and were approved by the… Read more about this study
- Who is it for?
- Any age
- Conditions the study is for
- Thymidine Kinase 2 Deficiency
- What is being tested?
- doxecitine and doxribtimine
- Type of treatment
- Pill or oral medicine
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 47 participants
- Where
- 8 sitesin 3 countries
- Study dates
- 5 Jul 2019to 26 Aug 2026
- Phase
- Phase 2
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages Any age
- All sexes
- No healthy volunteers
- Child, Adult, Older adult
Who may be able to join
- Signed informed consent by the parent(s) or legally authorized representative (LAR) and/or assent by the study participant (when applicable).
- Confirmed genetic mutation in the TK2 gene.
- Absence of other genetic disease or polygenic disease.
- Current treatment with nucleos(t)ides for TK2 deficiency. Study participants who were not previously enrolled in MT-1621-101 [NCT03701568] will require Sponsor approval to ensure that collection of clinical and functional measurements prior to treatment are sufficient to serve as baseline assessments for purposes of evaluating safety and efficacy.
- Female study participants must not be breastfeeding, have a negative pregnancy test at screening (females ≥10 years old), and have no intention to become pregnant during the course of the study. Female study participants who are of childbearing potential (ie, following menarche until ≥1 year post-menopausal if not anatomically and physiologically incapable of becoming pregnant) must agree and commit to the use of highly effective methods of birth control for the duration of the study and for 30 days after the end of the study. Acceptable methods are defined as those that result, alone or in combination, in a low failure rate (ie, <1% per year) when used consistently and correctly, such as surgical sterilization, an intrauterine device, or hormonal contraception in combination with a barrier method. In certain countries (if permitted by law), women of childbearing potential may instead agree to abide by heterosexual sexual abstinence during the study and for 30 days after the end of the study.
- Male study participants with sexual partners should use condoms for the duration of the study and for 30 days after the last dose of study drug to prevent passing study drug to the partner in the ejaculate. Male participants should be advised not to donate sperm for 30 days after the last dose of study drug.
- Willingness to maintain current treatment regimen and current exercise regimen for the duration of the clinical study.
- Willingness to comply with the study protocol, including but not limited to, all study procedures, study visits, and study drug compliance.
Who cannot join
- History of liver disease, or liver function test results (ALT, AST, or total bilirubin) ≥2× upper limit of normal without prior Sponsor approval.
- Other significant medical condition that, in the opinion of the Investigator or Study Sponsor, may confound interpretation of the clinical course of TK2 deficiency.
Trial locations and contacts
8 sites in 3 countries.
8 sites in 3 countries
Spain4 sites
Tk0102 3102
Barcelona
Tk0102 3121
Esplugues de Llobregat
Tk0102 3031
Madrid
Tk0102 3101
Seville
About this study
Official title: A Phase 2 Open-Label Study of Continuation Treatment With Combination Pyrimidine Nucleosides in Patients With Thymidine Kinase 2 Deficiency (TK2)
This is a Phase 2 prospective open-label treatment study of the safety and efficacy of doxecitine and doxribtimine in study participants with thymidine kinase 2 (TK2) deficiency who participated in the retrospective study MT-1621-101 [NCT03701568] or who were receiving nucleos(t)ide treatment and were approved by the Sponsor.
- Conditions
- Thymidine Kinase 2 Deficiency
- Being tested
- doxecitine and doxribtimine
- Keywords
- Thymidine Kinase 2 Deficiency, TK2d, mitochondrial disorder, mitochondrial disease, Mitochondria, deoxycytidine and deoxythymidine, doxecitine and doxribtimine, MT1621, primary mitochondrial myopathy, mitochondrial depletion syndrome, Muscle weakness, Muscle atrophy, Loss of mobility
- Medical subject headings
- Mitochondrial Diseases, Muscle Weakness, Muscular Atrophy
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
doxecitine and doxribtimineDrug
Also called MT1621, GMP grade dC/dT (deoxycytidine and deoxythymidine)
Doxecitine and doxribtimine is administered orally in 3 equal doses given approximately 6 to 8 hours apart. Doxecitine and doxribtimine is administered with food.
| Study group | Role | What they receive |
|---|---|---|
| doxecitine and doxribtimine | Experimental | This is an open label study with all participants in a single arm. Study participants will take doxecitine and doxribtimine up to a maximum of 800 mg/kg/day (400 mg/kg/day doxecitine and 400 mg/kg/day doxiribtimine). Receives: Drug: doxecitine and doxribtimine |
What is being measured
The primary outcome is the main question the study is designed to answer.
Incidence of treatment-emergent adverse events (TEAEs)
An AE is any untoward medical occurrence in a patient or clinical study participant, temporally associated with the use of study medication, whether or not considered related to the study medication.
Measured: From first administration of study drug until end of safety follow-up (up to approximately 7 years)
Incidence of TEAEs leading to study drug withdrawal
An AE is any untoward medical occurrence in a patient or clinical study participant, temporally associated with the use of study medication, whether or not considered related to the study medication.
Measured: From first administration of study drug until end of safety follow-up (up to approximately 7 years)
Secondary outcomes (4)
Clinical Global Impression of Improvement (CGI-I) Response score
The CGI-I rating scale permits a global evaluation by the clinician of the study participant's improvement over time after study drug has been initiated. Improvement in a study participant's condition is rated on a 7-point scale ranging from 1 (very much improved) to 7 (very much worse) as follows: 1 = very much improved, 2 = much improved, 3 = minimally improved, 4 = no change, 5 = minimally worse, 6 = much worse, and 7 = very much worse.
Measured: Assessed at end of study (approximately 7 years)
Mean minimum plasma concentration (Cmin) of deoxycytidine (dC) and deoxythymidine (dT) at steady state
Cmin = Minimum plasma concentration
Measured: Plasma samples will be collected at Months 1, 3, and 6
Mean maximum plasma concentration (Cmax) of dC and dT at steady state
Cmax = Maximum plasma concentration
Measured: Plasma samples will be collected at Months 1, 3, and 6
Mean area under the plasma concentration - time curve from time 0 to 24 hours (AUC0-24) of dC and dT at steady state
AUC0-24 = Area under the plasma concentration-time curve from 0 to 24 hours
Measured: Plasma samples will be collected at Months 1, 3, and 6
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted19 Feb 2019
- Study start5 Jul 2019
- Primary completion26 Aug 2026
- Study completion26 Aug 2026
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Publications (1)Papers the sponsor has linked to this study.
- Other trials for Thymidine Kinase 2 DeficiencyStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase 2
- Primary purpose
- Treatment
- Allocation
- Not applicable
- Intervention model
- Single group
- Masking
- None (open label)
- Enrolment
- 47 participants (actual)
Sponsor and investigators
- Lead sponsor
- UCB BIOSCIENCES, Inc.
- Sponsor type
- Industry (pharma, biotech, devices)
- Responsible party
- Sponsor
- Investigators
- UCB Cares, Study director, 001 844 599 2273
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT03845712
- Sponsor's protocol ID
- TK0102
- Other IDs
- 2018-004277-27, U1111-1304-0423, 2023-510427-29, 2023, 2018
- Acronym
- Continuation
- Status last verified
- Sep 2026
- First submitted
- 6 Feb 2019
- Last updated
- 8 Sep 2026
- Results posted
- No
- Data monitoring committee
- Yes
- FDA-regulated drug
- Yes
- FDA-regulated device
- No
- Individual data sharing
- Yes: Data from this trial may be requested by qualified researchers six months after product approval in the US and/or Europe, or global development is discontinued, and 18 months after trial completion. Investigators may request access to anonymized individual patient-level data and redacted trial documents which may include: analysis-ready datasets, study protocol, annotated case report form, statistical analysis plan, dataset specifications, and clinical study report. Prior to use of the data, proposals need to be approved by an independent review panel at www.Vivli.org and a signed data sharing agreement will need to be executed. All documents are available in English only, for a prespecified time, typically 12 months, on a password protected portal. This plan may change if the risk of re-identifying trial participants is determined to be too high after the trial is completed; in this case and to protect participants, individual patient-level data would not be made available.
- Expanded access
- Available
Publications
Hernandez-Voth A, Sayas Catalan J, Corral Blanco M, Castano Mendez A, Martin MA, De Fuenmayor Fernandez de la Hoz C, Villena Garrido V, Dominguez-Gonzalez C. Deoxynucleoside therapy for respiratory involvement in adult patients with thymidine kinase 2-deficient myopathy. BMJ Open Respir Res. 2020 Nov;7(1):e000774. doi: 10.1136/bmjresp-2020-000774.
PubMed 33246973
Study at a glance
From the registry record, last updated by the sponsor on 8 Sep 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- A Phase 2 Open-Label Study of Continuation Treatment With Combination Pyrimidine Nucleosides in Patients With Thymidine Kinase 2 Deficiency (TK2)
- ClinicalTrials.gov ID
- NCT03845712
- Acronym / sponsor ID
- Continuation / TK0102
- Conditions
- Thymidine Kinase 2 Deficiency
- Keywords
- Thymidine Kinase 2 Deficiency, TK2d, mitochondrial disorder, mitochondrial disease, Mitochondria, deoxycytidine and deoxythymidine, doxecitine and doxribtimine, MT1621
- Phase
- Phase 2
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 47 participants (actual)
- Lead sponsor
- UCB BIOSCIENCES, Inc.Industry (pharma, biotech, devices)
- Study start
- 5 Jul 2019 (actual)
- Primary completion
- 26 Aug 2026 (actual)
- Study completion
- 26 Aug 2026 (actual)
- First posted
- 19 Feb 2019 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
This is a Phase 2 prospective open-label treatment study of the safety and efficacy of doxecitine and doxribtimine in study participants with thymidine kinase 2 (TK2) deficiency who participated in the retrospective study MT-1621-101 [NCT03701568] or who were receiving nucleos(t)ide treatment and were approved by the Sponsor.
Study design
- Primary purpose
- Treatment
- Allocation
- Not applicable
- Intervention model
- Single group
- Masking
- None (open label)
- Number of arms
- 1
| Arm | Type | Receives |
|---|---|---|
| doxecitine and doxribtimine | Experimental | Drug: doxecitine and doxribtimineThis is an open label study with all participants in a single arm. Study participants will take doxecitine and doxribtimine up to a maximum of 800 mg/kg/day (400 mg/kg/day doxecitine and 400 mg/kg/day doxiribtimine). |
Who may qualify
- Sex
- All
- Healthy volunteers
- Not accepted
- Age groups
- Child, Adult, Older adult
Key inclusion criteria (8 listed)
- Signed informed consent by the parent(s) or legally authorized representative (LAR) and/or assent by the study participant (when applicable).
- Confirmed genetic mutation in the TK2 gene.
- Absence of other genetic disease or polygenic disease.
- Current treatment with nucleos(t)ides for TK2 deficiency. Study participants who were not previously enrolled in MT-1621-101 [NCT03701568] will require Sponsor approval to ensure that collection of clinical and functional measurements prior to treatment are sufficient to serve as baseline assessments for purposes of evaluating safety and efficacy.
- Female study participants must not be breastfeeding, have a negative pregnancy test at screening (females ≥10 years old), and have no intention to become pregnant during the course of the study. Female study participants who are of childbearing potential (ie, following menarche until ≥1 year post-menopausal if not anatomically and physiologically incapable of becoming pregnant) must agree and commit to the use of highly effective methods of birth control for the duration of the study and for 30 days after the end of the study. Acceptable methods are defined as those that result, alone or in combination, in a low failure rate (ie, <1% per year) when used consistently and correctly, such as surgical sterilization, an intrauterine device, or hormonal contraception in combination with a barrier method. In certain countries (if permitted by law), women of childbearing potential may instead agree to abide by heterosexual sexual abstinence during the study and for 30 days after the end of the study.
Key exclusion criteria (2 listed)
- History of liver disease, or liver function test results (ALT, AST, or total bilirubin) ≥2× upper limit of normal without prior Sponsor approval.
- Other significant medical condition that, in the opinion of the Investigator or Study Sponsor, may confound interpretation of the clinical course of TK2 deficiency.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| doxecitine and doxribtimineAlso: MT1621, GMP grade dC/dT (deoxycytidine and deoxythymidine)Doxecitine and doxribtimine is administered orally in 3 equal doses given approximately 6 to 8 hours apart. Doxecitine and doxribtimine is administered with food. | Drug | doxecitine and doxribtimine |
Primary outcome
Incidence of treatment-emergent adverse events (TEAEs)
Time frame: From first administration of study drug until end of safety follow-up (up to approximately 7 years)
An AE is any untoward medical occurrence in a patient or clinical study participant, temporally associated with the use of study medication, whether or not considered related to the study medication.
Incidence of TEAEs leading to study drug withdrawal
Time frame: From first administration of study drug until end of safety follow-up (up to approximately 7 years)
An AE is any untoward medical occurrence in a patient or clinical study participant, temporally associated with the use of study medication, whether or not considered related to the study medication.
4 secondary outcomes
Clinical Global Impression of Improvement (CGI-I) Response score
Time frame: Assessed at end of study (approximately 7 years)
Mean minimum plasma concentration (Cmin) of deoxycytidine (dC) and deoxythymidine (dT) at steady state
Time frame: Plasma samples will be collected at Months 1, 3, and 6
Mean maximum plasma concentration (Cmax) of dC and dT at steady state
Time frame: Plasma samples will be collected at Months 1, 3, and 6
Mean area under the plasma concentration - time curve from time 0 to 24 hours (AUC0-24) of dC and dT at steady state
Time frame: Plasma samples will be collected at Months 1, 3, and 6
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 8 Sep 2026.
- Derived from this study: PubMed 33246973Hernandez-Voth A, Sayas Catalan J, Corral Blanco M, Castano Mendez A, Martin MA, De Fuenmayor Fernandez de la Hoz C, Villena Garrido V, Dominguez-Gonzalez C. Deoxynucleoside therapy for respiratory involvement in adult patients with thymidine kinase 2-deficient myopathy. BMJ Open Respir Res. 2020 Nov;7(1):e000774. doi: 10.1136/bmjresp-2020-000774.
- Individual participant dataSharing planned: Yes. Data from this trial may be requested by qualified researchers six months after product approval in the US and/or Europe, or global development is discontinued, and 18 months after trial completion. Investigators may request access to anonymized individual patient-level data and redacted trial documents which may include: analysis-ready datasets, study protocol, annotated case report form, statistical analysis plan, dataset specifications, and clinical study report. Prior to use of the data, proposals need to be approved by an independent review panel at www.Vivli.org and a signed data sharing agreement will need to be executed. All documents are available in English only, for a prespecified time, typically 12 months, on a password protected portal. This plan may change if the risk of re-identifying trial participants is determined to be too high after the trial is completed; in this case and to protect participants, individual patient-level data would not be made available.
Related trials for Thymidine Kinase 2 Deficiency
RecruitingPhase 2
Doxecitin and Doxribthymine in Adult Subjects With Thymidine Kinase 2 (TK2) Deficiency
Thymidine Kinase 2 (TK2 ) Deficiency, Mitochondrial Myopathies
Active, not recruitingPhase 1/2
Treatment of TK2 Deficiency With Thymidine and Deoxycytidine
Mitochondrial DNA Depletion Syndrome 2 Myopathic Type, Thymidine Kinase 2 Deficiency
Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
UCB Cares study director
001 844 599 2273
8 sites in 3 countries: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A Phase 2 study testing doxecitine and doxribtimine in people with Thymidine Kinase 2 Deficiency, run by UCB BIOSCIENCES, Inc. at 8 sites in 3 countries.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 8 inclusion and 2 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 8 Sep 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 8 sites in Spain, Israel, United States. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
What does this phase mean?
Phase 2 studies give the treatment to a larger group to see whether it has the intended effect and to keep checking safety.
Not every study follows the same path, and some studies (observational studies, device studies) have no phase.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Incidence of treatment-emergent adverse events (TEAEs) (time frame: From first administration of study drug until end of safety follow-up (up to approximately 7 years)). The study lists 2 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
On the ClinicalTrials.gov record for NCT03845712, which also lists 1 linked publication.
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 8 Sep 2026.