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FDA Approves 1st Drug for Thymidine Kinase 2 Deficiency, a Very Rare Mitochondrial Disease
Action
The U.S. Food and Drug Administration (FDA) approved Kygevvi (doxecitine and doxribtimine) powder to treat thymidine kinase 2 deficiency (TK2d) in adults and pediatric patients who start to show symptoms when they are 12 years old or younger. Kygevvi received Breakthrough Therapy Designation for this indication.
Disease or Condition
TK2d is a rare, inherited genetic disorder that affects the body's ability to produce and repair mitochondrial DNA (mtDNA). Conditions that cause low levels of mtDNA, including TK2d, can be called mitochondrial depletion syndromes. Symptoms of TK2d can include muscle weakness and respiratory (breathing) failure. While the exact frequency of TKd2 is not known, it is considered very rare. Approximately 120 patients have been described in the medical literature, although the condition may be underdiagnosed.
Data Supporting Kygevvi
The efficacy of Kygevvi to treat patients with TK2d who start to show symptoms when they are 12 years old or younger was established based on data from one phase 2 clinical study, two retrospective chart review studies, and an expanded access program. The survival in patients treated with Kygevvi was compared with the survival in an untreated external control group composed of untreated patients from published literature and one of the retrospective studies in this drug development program.
Survival analysis for 78 matched pairs of treated and untreated patients showed there were three deaths (4%) in the patients receiving Kygevvi compared with 28 deaths (36%) in the external control group. Mean survival time at 10 years was 9.6 years for the group receiving Kygevvi compared with 5.7 years in the control group.
Safety
The most common side effects of Kygevvi are diarrhea, vomiting, increase in liver enzymes, and abdominal pain.
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