The U.S. Food and Drug Administration (FDA) has approved Kygevvi (doxecitine and doxribtimine) for children and adults with Thymidine Kinase 2 deficiency (TK2d), according to a press release.
“The approval of doxecitine and doxribtimine represents a pivotal moment for the TK2d community who previously had no FDA-approved treatment,” stated Donatello Crocetta, chief medical officer at UCB, the pharmaceutical company that owns the therapy.
The drug is approved for individuals whose symptom onset occurred at or before 12 years of age. It will be available as a powder that is mixed with water to create an oral solution.
Individuals with TK2d produce insufficient levels of mitochondrial DNA due to mutations in the TK2 gene, leading to severe, progressive muscle weakness. The goal of this therapy is to incorporate the DNA building blocks deoxycytidine and deoxythymidine into the mitochondrial DNA of the skeletal muscle.
Approval was granted based on analysis of 82 patients who received doxecitine and doxribtimine. Compares with untreated patients, treated individuals had an 86% lower overall mortality risk from treatment start. Patients were treated for a median of four years and had a median age of symptom onset of 1.5 years.
Common side effects included gastrointestinal complaints such as vomiting, diarrhea and upper abdominal pain. Some individuals experienced increased liver enzymes as well.
“It’s hard to overstate the importance of this FDA approval for those diagnosed with TK2d,” said Kristen Clifford, president and chief executive officer at the United Mitochondrial Disease Foundation. “For too long, caregivers and their families have had to endure the burden of this disease.”
Doxecitine and doxribtimine have received several designations from the FDA, including Orphan Drug, Breakthrough, Priority Review and Rare Pediatric Disease designations. Kygevvi is expected to be commercially available in the US by the first quarter of 2026.
The combination therapy is currently under review by the European Medicines Agency.