Positives

• Patients with TK2d treated with doxecitine and doxribtimine showed an approximately 86% reduction in overall risk of death compared with the natural-history cohort, with sustained motor and respiratory benefit over follow-up FDA.
  
  
• A patient on long-term Kygevvi treatment regained the ability to walk independently and reduced ventilator dependence, supporting the mechanism of restoring mitochondrial nucleotide pools NeurologyLive.
  
  

Negatives

• Patients commonly developed elevated liver transaminases on Kygevvi, requiring routine LFT monitoring throughout therapy FDA.
  
  
• Several trial participants experienced diarrhea and vomiting severe enough to lead to hospitalization, dose reduction, or permanent discontinuation Pulmonology Advisor.
  
  

Hurdles & Side Effects

• Kygevvi is FDA-approved only for genetically confirmed TK2 deficiency, so Long COVID patients with mitochondrial-dysfunction phenotypes have no labeled access pathway and would face near-total off-label denial from insurers UCB.
  
  
• As an ultra-rare disease therapy from UCB, the drug carries six-figure-per-year list pricing typical of nucleoside replacement programs, putting it well outside cash-pay reach for off-label exploration Pharmaceutical Technology.
  
  
• UCB expects commercial availability only from Q1 2026 onward, with distribution through specialty pharmacy and likely a confirmed-diagnosis gating step before any prescription will dispense PR Newswire.