Evaluation of the efficacy and safety of stiripentol in patients 6 years and older with primary hyperoxaluria type 1, 2 or 3.

A multicenter randomized, double-blind, placebo-controlled phase 3 study The study is designed to compare the efficacy of stiripentol to a placebo in patients 6 years and older with primary hyperoxaluria type 1, 2 or 3.

The study will be conducted in 2 periods: a 6-month, placebo-controlled, double-blind treatment period (period 1) followed by a 6-month open-label treatment period with blind maintained on results (period 2).

Patients who benefit from the treatment after the first 12 months of study treatment will be proposed to enter the open-label extension (OLE) part of the study to continue to assess the long-term efficacy and safety of stiripentol.

Screening Criteria :

• 1. Male or female patients aged ≥ 6 years at the time of consent signature
• 2. Diagnosed with primary hyperoxaluria (type 1, 2 or 3) documented as per standard methods
• 3. With last estimated Glomerular Filtration Rate ≥ 45 mL/min/1.73 m2
• 4. Able to understand and willing to comply with study requirements and to provide written informed consent. In case of patient under the age of legal consent, the legal guardian(s) must provide informed consent and the patient should provide assent as per local and national requirements
• 5. Female patients with contraception (intrauterine device, intrauterine hormone-releasing system, bilateral tubal occlusion, surgical sterilization of male partner, established use of oral, implantable, injectable, or transdermal hormonal methods of contraception, a double-barrier method (combination of male condom with cap, diaphragm, or sponge, in conjunction with spermicide) or true sexual abstinence

Inclusion Criteria:

• 1. Diagnosed with primary hyperoxaluria disease and subtype (type 1, 2 or 3) confirmed by genetic testing
• 2. Receiving optimal management of the disease through standard of care strategies (e.g., increased fluid intake, vitamin B6, potassium citrate) with or without approved target medications (e.g., lumasiran). Patients not receiving lumasiran can only be enrolled if they are not eligible for treatment with lumasiran for the specific following reasons: contraindications, previous treatment discontinued due to lack of efficacy or poor tolerability, not meeting national or regional eligibility criteria for treatment, investigator judgement
• 3. With mean 24-hour urinary oxalate excretion from 2 valid 24-hour urine collections ≥ 0.70 mmol/24h/1.73m²
• 4. With estimated Glomerular Filtration Rate ≥ 45 mL/min/1.73 m2 (Schwartz et al., 2009 in pediatric patients and CKD-EPI in adults)
• 5. Pubescent and adult female patients must have a negative urine or serum pregnancy test within 60 days prior to first dose of study treatment if of childbearing potential. If the urine pregnancy test is positive or cannot be confirmed as negative, a serum pregnancy test will be required. The serum pregnancy test must be negative for the patient to be eligible
• 6. In France, patient affiliated with or who benefits from a social security scheme

Exclusion Criteria:

• 1. Any relevant change in the use of any component of the standard of care (fluid intake, vitamin B6, potassium citrate) in the 4 weeks prior to inclusion or if such change is planned to occur during the first 6 months of the study

• 2. If under approved targeted medications (e.g., lumasiran), treatment should have been administered for at least 6 months, with no change in dose or regimen in the 3 months prior to inclusion or ifsuch change is planned it should not occur during the first 12 months of the study

• 3. History of kidney or liver transplant

• 4. Presenting any of the following liver function tests abnormalities during the screening period:

  1. Alanine aminotransferase (ALT) or aspartate aminotransferase (AST)> 2 × upper limit of normal (ULN)
  2. Total bilirubin > 1.5 x ULN. Patients with elevated total bilirubin that is secondary to documented Gilbert's syndrome are eligible if the total bilirubin is < 2 x ULN

• 5. Recent (4 weeks before the screening visit) or planned change in eating habits

• 6. Intermittent fasting planned during the 6 first months of the study period (e.g., Ramadan)

• 7. Other medical conditions or comorbidities, treatment, which in the opinion of the investigator, would interfere with study compliance or data interpretation

• 8. Presenting any significant biological or clinical anomalies that are not compatible with participation in the study according to the investigator

• 9. History of severe allergy, asthma, skin rashes, intolerance to lactose or hypersensitivity to the study treatments

• 10. Treatment affecting hepatic metabolism (i.e., cimetidine, ketoconazole, fluconazole, itraconazole, phenytoin, rifampicin, rifabutin) that is ongoing or has been taken in the month prior to the selection visit

• 11. Treatment affecting the renal tubule (probenecid, β-lactam, etc.,) that is ongoing or has been taken in the two weeks prior to the start of the study

• 12. Contraindications to stiripentol as defined in the applicable Investigator's Brochure (i.e. patients presenting a hypersensitivity to the active substance or any excipients)

• 13. Patient at risk of pregnancy, pregnant or breastfeeding female

• 14. Patient under guardianship or curatorship

• 15. Patient under the protection of the Court or deprived of liberty

• 16. Patient participating in another interventional clinical trial which could interfere with the trial's results or impact the other trial's results; or within the last 30 days or 5 half-lives of the study investigational treatment, whichever is longer, prior to the urinary sampling during the screening period, or are in follow-up of another clinical study prior to randomization

• 17. Patient whose current state of health does not allow him/her to give consent

All Sponsor personnel will be blinded to study drug treatment until the 6-month treatment period data is unblinded for the primary analysis. To ensure that blinding will be maintained along the study, the following measures are implemented:

• the capsules are identical for both products
• all packaging items, bottles (primary packagings) and boxes (secondary, tertiary and quaternary packagings) are identical bearing similar study specific labels.

At the start of the open-label Period 2), in order to maintain the blind to treatment assignment, gradual initiation of treatment will be done in all patients over the first three days as follows: 30 mg/kg/day at Day1, 40 mg/kg/day at Day 2 and 50 mg/kg/day from Day 3 (with a maximum dose of 3,000 mg/day).