What Was Approved?
On November 3, 2025, the U.S. Food and Drug Administration approved Kygevvi (doxecitine and doxribtimine) for the treatment of thymidine kinase 2 deficiency, or TK2d, in adults and pediatric patients whose symptoms began at 12 years of age or younger.
Kygevvi is the first FDA-approved treatment specifically for TK2d.
What Is TK2 Deficiency?
TK2d is a rare inherited mitochondrial disorder.
It affects the body’s ability to maintain mitochondrial DNA and can lead to problems such as:
- Progressive muscle weakness
- Difficulty walking
- Breathing problems
- Other neuromuscular complications
Disease severity can vary substantially among patients.
How Is Kygevvi Taken?
Kygevvi is an oral powder that is mixed with water.
The total daily dose is based on body weight and is divided into three equal doses taken with food throughout the day.
Treatment begins at a lower dose and is increased according to the FDA-approved dosing schedule.
What Did the Clinical Evidence Show?
FDA evaluated data from clinical studies, retrospective patient records, and an expanded access program.
In the main survival analysis:
- 3 of 78 treated patients (4%) died
- 28 of 78 matched untreated patients (36%) died
Because the comparison included an external untreated control group rather than a randomized placebo group, the results should be interpreted within that study design.
What Are the Main Side Effects?
Common adverse reactions included:
- Diarrhea
- Abdominal pain
- Vomiting
- Increased liver enzymes
Liver tests should be checked before treatment and monitored during therapy.
Bottom Line
Kygevvi (doxecitine and doxribtimine) is the first FDA-approved treatment for TK2 deficiency in patients whose symptoms began at age 12 or younger.
It is taken orally in three divided daily doses and requires monitoring for gastrointestinal adverse effects and liver enzyme elevations.
Sources
- U.S. Food and Drug Administration (FDA) — FDA Approves 1st Drug for Thymidine Kinase 2 Deficiency, a Very Rare Mitochondrial Disease, November 3, 2025.
- U.S. Food and Drug Administration (FDA) — Drug Trials Snapshot: Kygevvi.
- U.S. Food and Drug Administration (FDA) — Kygevvi Prescribing Information, 2025.