Chiesi Global Rare Diseases, a business unit of the Italian Chiesi Group, has received FDA priority review for its evaluation of idebenone, intended for the treatment of Leber Hereditary Optic Neuropathy (LHON).
Let’s start with Chiesi.
Headquartered in Parma, Italy, Chiesi Group is a research-focused international biopharmaceutical company developing and manufacturing therapeutics for respiratory health, rare diseases, and specialty care.
- The company operates seven research and development centers across the globe: Italy, France, the United States, China, the United Kingdom, and Sweden.
And within this company?
The Chiesi Global Rare Diseases business unit refers to itself as a “family-owned,” Certified B Corporation specializing in developing a portfolio of rare disease-targeted therapeutics in areas such as:
- Dermatology
- Endo-metabolic
- Hematology
- Immunodeficiences
- Ophthalmology
See the full pipeline and areas of research here
- To note: These therapeutics range from the preclinical stage to regulatory approval.
Now to LHON.
LHON is a mitochondrially-inherited degeneration of retinal ganglion cells (RGCs) that leads to reduced adenosine triphosphate (ATP) generation and increased oxidative stress.
The result: Acute central vision loss.
And this targeted drug in question?
Idebenone is a synthetic analogue of ubiquinone, which is described as a “vital cell antioxidant and essential component of the electron transport chain (ETC).”
- See here for a rundown on ETC, which, essentially, leads to the creation of ATP.
What it does for LHON: Targets mitochondrial dysfunction of RGCs (also known as the underlying cause of LHON).
- The clinical thought: Via an interaction with ETC, idebenone increases and improves ATP production needed for mitochondrial function, as well as reduces oxidative damage (among other protective functions).
And its potential beyond LHON: Extends to potentially treating cognitive disorders such as Alzheimer's disease.
And its current regulatory status?
Outside the U.S., idebenone has received approval for use by the European Medicines Agency (EMA) for the treatment of visual impairment in adolescent and adult patients diagnosed with LHON.
- The brand name: Raxone.
- Its dosage form: Oral administration via tablets.
Those ex-EU countries with approval:
- Switzerland (2014)
- UK (in 2015)
- Israel (in 2017)
- South Korea (in 2019)
- Serbia (2019)
- Chile (2024)
- Bahrain (2025)
- Taiwan (2025)
Next: Idebenone in the United States.
So far: Idebenone has received Orphan Drug Designation for LHON.
And most recently: The FDA has accepted the therapeutic’s new drug application (NDA) for review based on clinical data from both phase 3 and phase 4 clinical trials.
Let’s talk about this research.
On the phase 3 front: RHODOS was a randomized, placebo-controlled trial (NCT00747487) evaluating the efficacy of idebenone versus a placebo among 85 LHON patients (aged 14 to 65).
- The primary endpoint: Best recovery of logMAR visual acuity, determined by a change from baseline to week 24 in the eye showing the most improvement or least deterioration
The findings: Idebenone-treated patients had a logMAR of -0.136 with an improvement by about 6 letters on the Early Treatment Diabetic Retinopathy Study (ETDRS) chart versus placebo (which had a logMAR of -0.036 and an estimated 1-letter improvement [p = 0.0862]).
- See here for secondary outcomes (and the results here).
How about the phase 4 data?
That would be the LEROS study, an open-label interventional trial (NCT02774005) that evaluated the efficacy and safety of idebenone as long-term treatment among 199 LHON patients (aged 12+).
- Specifically, these patients were started on idebenone within ≤1 year of symptom onset and compared to a matched external natural history control group.
The primary endpoint: The number of eyes achieving a clinically relevant benefit (CRB)—clinically relevant recovery (CRR)—by month 12 of treatment (while secondary endpoints involved clinically relevant stabilization [CRS]).
And the findings?
- By month 12: A total of 42.3% of eyes from the idebenone group achieved a CRB compared to just 20.7% in the control group (odds ratio [OR], 2.29; P =.002).
- By month 24: CRB was sustained by 52.9% of eyes in the idebenone group versus 36% in the control group (OR 2.08; p = 0.0297).
See here for secondary analysis data and here for post-hoc responder analysis findings.
Take note: The most common adverse reactions to occur (incidence ≥3%) were alanine aminotransferase, diarrhea, and an increase in aspartate aminotransferase, with generally mild-to-moderate severity and rarely needing treatment discontinuation.
Duly noted. So! What does this priority review mean for idebenone in the U.S.?
Priority review essentially accelerates the FDA review process for a drug intended to treat certain serious or life-threatening diseases (such as LHON, in this case) and illnesses.
- Under this, the target timeline is shortened to 6 months (versus the standard 10-month period)
Specifically, this is given to drugs that could potentially offer significant improvements in safety or effectiveness over existing treatments.
And last question … when do we expect to hear the FDA’s decision?
The federal agency assigned a Prescription Drug User Fee Act (PDUFA) target action date of Feb. 28, 2026.
Its potential significance: As Chiesi noted, idebenone could be the first and only clinically proven therapeutic in the U.S. designed to target the underlying cause of LHON.