New TK2d treatment available through UK early access scheme

2 September 2026

A new treatment for TK2d is now available in the UK through the Early Access to Medicines Scheme. Doxecitine-doxribtimine is the first medicine developed specifically to target the underlying cause of TK2d. While not yet fully licensed in the UK, the scheme allows certain patients to access the treatment while it continues through the UK’s licensing process.

For the first time, some people with a type of mitochondrial disease called thymidine kinase 2 deficiency, or TK2d, may now be able to access a new treatment designed specifically for their condition through something called the Early Access to Medicines Scheme (EAMS).

The treatment, called doxecitine-doxribtimine, is already approved in the USA and EU under the brand name Kygevi, but is yet to be fully licensed in the UK.

What families need to know

Although doxecitine-doxribtimine (sometimes referred to as dC/dT)  isn’t yet fully licensed in the UK, some children and adults with genetically confirmed TK2d may now be able to access it through the UK’s Early Access to Medicines Scheme if their symptoms began at or before the age of 12. This refers to the age when symptoms first appeared, not the person’s current age.

Families should speak to their mitochondrial specialist team, as access cannot be arranged directly through The Lily Foundation or via the manufacturer.

What is doxecitine-doxribtimine?

Doxecitine-doxribtimine is the first medicine developed to target the underlying cause of thymidine kinase 2 deficiency, usually shortened to TK2d. While not a cure, it aims to address the specific biological problem that leads to the condition.

It provides substances that the body uses to make and maintain mitochondrial DNA. This may help muscle cells produce energy more effectively and could slow the progression of the condition.

Evidence so far suggests that the treatment may improve survival and help some patients maintain or regain physical abilities. However, TK2d is extremely rare, and the evidence comes from a relatively small number of patients, so people receiving it will continue to be monitored carefully.

What is TK2d?

TK2d is a very rare inherited mitochondrial disease. It mainly affects the muscles and can cause progressive muscle weakness, loss of movement, breathing difficulties and problems with eating and swallowing.

The condition affects people in different ways and can be life-limiting, particularly when symptoms begin in infancy or childhood.

You can find more information about its causes, symptoms, diagnosis and management on our TK2d information page.

What is the Early Access to Medicines Scheme?

Before a treatment can be routinely prescribed on the NHS in the UK, it must receive a licence.

The Early Access to Medicines Scheme allows some patients with serious or life-threatening conditions to access promising new medicines before they receive a full UK marketing authorisation, where there’s a clear unmet medical need and the potential benefits outweigh the risks.

The UK medicines regulator, the MHRA, has reviewed the available evidence and believes the potential benefits of doxecitine-doxribtimine are greater than the known risks for patients who meet the scheme’s criteria.

A positive EAMS decision is not the same as full UK approval, however, and it doesn’t mean that everyone with TK2d will be eligible for and benefit from the treatment.

You can read the official MHRA information about doxecitine-doxribtimine and TK2d on the GOV.UK website.

Could this treatment help people with other mitochondrial diseases?

Doxecitine-doxribtimine has been developed specifically for TK2d. It works by addressing the particular problem caused by changes in the TK2 gene.

Other mitochondrial diseases are caused by different genetic changes and affect the mitochondria in different ways. There’s currently no evidence that this treatment would be safe or effective for those conditions.

This early access scheme is therefore limited to eligible people with genetically confirmed TK2d and cannot be used to provide the treatment for other forms of mitochondrial disease.

Why is it approved in the USA and Europe, but not here?

Medicines must be assessed separately by the regulators responsible for different countries and regions.

Doxecitine-doxribtimine was approved in the United States in November 2025 and in the European Union in March 2026. Following the UK’s departure from the European Union, EU approval doesn’t automatically apply here.

The drug still needs to go through a separate UK approval process. EAMS provides a route for some eligible patients to access it while it remains unlicensed here.

What happens next?

Specialist mitochondrial disease teams can now consider whether eligible patients may be suitable for treatment.

Patients who receive doxecitine-doxribtimine through EAMS will need regular monitoring, which may include blood tests and other checks recommended by their clinical team.

Further decisions will be needed before the treatment can become fully licensed and routinely available through the NHS. There’s no confirmed timetable for this yet.

What is The Lily Foundation’s role?

The Lily Foundation has worked with people affected by TK2d and organisations in the UK and internationally to make sure patients’ experiences are understood as this treatment has developed.

This has included gathering evidence about the impact of TK2d on patients and carers, and helping to make sure their experiences inform decisions about access to treatment. You can read more about our work to amplify the voices of people affected by TK2d.

We’ll continue to provide clear information, support families and represent the mitochondrial disease community as decisions are made about longer-term UK access.

The Lily Foundation cannot decide whether someone is eligible for doxecitine-doxribtimine, prescribe the treatment or guarantee access. These decisions must be made by a patient’s specialist clinical team.

How can patients and families access the drug?

Families should speak to their mitochondrial specialist team.

A specialist doctor will need to confirm whether the patient meets the EAMS criteria and whether the treatment is suitable for them.

Anyone affected by TK2d who would like more information or support can contact Katie, our Head of Patient Support and Advocacy, at katie@thelilyfoundation.org.uk.

Questions about individual patient treatment should always be discussed with your mitochondrial specialist.