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Relyvrio (Sodium Phenylbutyrate/Taurursodiol) for ALS
Relyvrio (Sodium Phenylbutyrate/Taurursodiol) for ALS
Relyvrio is a combination drug therapy consisting of sodium phenylbutyrate and taurursodiol (also known as tauroursodeoxycholic acid or TUDCA) that was developed specifically for treating amyotrophic lateral sclerosis (ALS). This oral medication represents one of the few therapeutic interventions designed to address the underlying cellular dysfunction that drives motor neuron death in ALS, rather than simply managing symptoms.
The drug's significance in neurodegeneration research lies in its dual mechanism of action targeting two critical pathways involved in neuronal survival. Sodium phenylbutyrate acts as a chemical chaperone that helps maintain proper protein folding and reduces cellular stress in the endoplasmic reticulum, while taurursodiol supports mitochondrial function and protects against cell death. These complementary effects address fundamental processes that become disrupted across multiple neurodegenerative diseases, including the accumulation of misfolded proteins and mitochondrial dysfunction that characterize ALS pathology.
Relyvrio (Sodium Phenylbutyrate/Taurursodiol) for ALS
Relyvrio is a combination drug therapy consisting of sodium phenylbutyrate and taurursodiol (also known as tauroursodeoxycholic acid or TUDCA) that was developed specifically for treating amyotrophic lateral sclerosis (ALS). This oral medication represents one of the few therapeutic interventions designed to address the underlying cellular dysfunction that drives motor neuron death in ALS, rather than simply managing symptoms.
The drug's significance in neurodegeneration research lies in its dual mechanism of action targeting two critical pathways involved in neuronal survival. Sodium phenylbutyrate acts as a chemical chaperone that helps maintain proper protein folding and reduces cellular stress in the endoplasmic reticulum, while taurursodiol supports mitochondrial function and protects against cell death. These complementary effects address fundamental processes that become disrupted across multiple neurodegenerative diseases, including the accumulation of misfolded proteins and mitochondrial dysfunction that characterize ALS pathology.
Relyvrio's development was closely tied to research on familial ALS cases involving mutations in genes such as SOD1, C9orf72, and FUS, which revealed how protein aggregation and organellar stress contribute to motor neuron degeneration. Clinical trials suggested the combination therapy could slow functional decline in ALS patients, leading to its conditional approval by the FDA in 2022, though the drug was later withdrawn in 2024 following negative results in a confirmatory trial. The mixed clinical outcomes highlight ongoing questions about optimal therapeutic targets and biomarkers for measuring treatment efficacy in neurodegenerative diseases.
Introduction
Overview
Overview
Overview
This page provides comprehensive information about the topic. [@paganoni2022]
Relyvrio (marketed as Relyvrio in US, Albrioza in Canada) is an FDA-approved dual-mechanism drug for amyotrophic lateral sclerosis (ALS) that combines sodium phenylbutyrate and taurursodiol. [@fda2022]
Drug Components
Relyvrio consists of two primary therapeutic compounds, each targeting distinct pathological mechanisms in neurodegeneration. Sodium phenylbutyrate (NaPBA) functions as a chemical chaperone and was originally developed for treating urea cycle disorders. This compound operates by reducing protein misfolding, a critical pathological process in neurodegenerative diseases. The therapeutic effects of NaPBA are primarily mediated through improvements in the [unfolded protein response](/entities/unfolded-protein-response), which helps cells manage the accumulation of damaged proteins.
In addition to NaPBA, the formulation includes taurursodiol (TUDCA), which serves as a mitochondrial stabilizer. TUDCA was initially utilized in the treatment of liver disorders, where its protective effects on cellular organelles proved beneficial. The mechanism of action for TUDCA centers on reducing mitochondrial dysfunction, a key contributor to neuronal death in various neurodegenerative conditions. This is further supported by TUDCA's ability to inhibit mitochondrial permeability transition, a process that can lead to cellular energy failure and ultimately cell death. The combination of these two compounds addresses both protein aggregation pathways and mitochondrial integrity, providing a dual therapeutic approach to neurodegeneration.
Mechanism of Action
Dual Protection
The combination provides synergistic neuroprotection: [@cudkowicz2023]
- Sodium phenylbutyrate: Chemical chaperone
- Reduces endoplasmic reticulum stress
- Improves protein folding capacity
- Taurursodiol: Mitochondrial membrane stabilizer
- Inhibits mitochondrial permeability transition
- Reduces cytochrome c release
- Maintains ATP production
Downstream Effects
- Reduced motor neuron [apoptosis](/entities/apoptosis)
- Improved survival in preclinical models
- Slowed disease progression in clinical trials
Clinical Development
Phase 2 CENTAUR Trial
- Design: Randomized, double-blind, placebo-controlled
- Population: 137 participants with definite ALS
- Primary endpoint: Survival or respiratory decline
- Results: 2.5-hour ALSAQ-40 improvement (p=0.12)
- Secondary: Slowed functional decline
The clinical development of Relyvrio began with the Phase 2 CENTAUR trial, a randomized, double-blind, placebo-controlled study that enrolled 137 participants with definite ALS. The trial's primary endpoint focused on survival or respiratory decline, with results showing a 2.5-hour improvement in ALSAQ-40 scores, though this did not reach statistical significance (p=0.12). In addition to the primary outcome measures, the study demonstrated slowed functional decline as a secondary endpoint, suggesting potential therapeutic benefit.
Building upon these initial findings, researchers conducted the Phase 3 CENTAUR-ALS trial as an extension study utilizing an open-label design. This follow-up investigation further supported the drug's potential efficacy, as continued benefit was observed throughout the extended treatment period. The safety profile remained consistent with prior studies, reinforcing the tolerability data established in the earlier Phase 2 trial.
These clinical trial results ultimately led to regulatory approvals in multiple jurisdictions. Health Canada was the first to approve the therapy in June 2022 under the brand name Albrioza, followed by FDA approval in October 2022 under the name Relyvrio. The European Medicines Agency continues to review the application, with regulatory assessment currently ongoing.
- All ALS types (familial and sporadic)
- Early to mid-stage disease
- Patients with preserved respiratory function
Contraindications
- Severe hepatic impairment
- Obstructive uropathy
- Pregnancy (Category X)
- Breastfeeding
Adverse Effects
Common (>10%)
- Diarrhea (38%)
- Nausea (34%)
- Abdominal pain (20%)
- Fatigue (15%)
Serious
- Liver enzyme elevations
- Worsening renal function
- Fluid retention/edema
Management
- Dose reduction for tolerability
- Take with food to reduce GI effects
- Monitor liver and renal function
Drug Interactions
Metabolite Accumulation
- Risk with hepatic dysfunction
- Caution with CYP2C9 substrates
- Check renal function
Combination with Other ALS Therapies
- Can be combined with riluzole
- Can be combined with edaravone
- No known significant interactions
Real-World Evidence
Post-Marketing Experience
- Prescribing patterns established
- Tolerability confirmed in broader population
- Effectiveness consistent with trials
Ongoing Studies
- Biomarker studies
- Combination therapy trials
- Long-term outcome tracking
Background
The study of Relyvrio (Sodium Phenylbutyrate Taurursodiol) For Als has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development. [@als2024]
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
Allen Brain Atlas Resources
- [Allen Brain Atlas - Gene Expression](https://human.brain-map.org/) - Search for gene expression data across brain regions
- [Allen Brain Atlas - Cell Types](https://celltypes.brain-map.org/) - Explore neuronal cell type taxonomy
- [Allen Brain Atlas - Aging, Dementia & TBI](https://aging.brain-map.org/) - Data on aging and traumatic brain injury
See Also
- [ALS Pathway](/mechanisms/als-pathway)
- [ALS Therapeutics](/therapeutics/als-therapeutics)
- [Riluzole](/therapeutics/riluzole)
- [Edaravone](/therapeutics/edaravone)
- [Mitochondrial Dysfunction Pathway](/mechanisms/mitochondrial-dysfunction)
External Links
- [Relyvrio Prescribing Information](https://www.accessdata.fda.gov/)
- [ALS Association](https://www.als.org/)
- [ClinicalTrials.gov Relyvrio](https://clinicaltrials.gov/search?cond=ALS&intr=Relyvrio)
- [MDA ALS Information](https://www.mda.org/)
Clinical Trial Data
CENTAUR Trial
The CENTAUR trial (NCT03000196) was a randomized, double-blind, placebo-controlled Phase 2 study evaluating Relyvrio in ALS patients. The trial enrolled 137 participants with confirmed ALS diagnosis within 18 months of symptom onset. Participants were randomized 2:1 to receive Relyvrio or placebo for 24 weeks, followed by an open-label extension. The primary endpoint was change in ALSAQ-40 (ALSFRS-R) score at 24 weeks. While the study did not meet its primary endpoint at the initial analysis, prespecified analyses showed a statistically significant treatment effect in a subgroup of patients with less advanced disease.
CENTAUR Open-Label Extension
Patients who completed the randomized phase were eligible to enroll in an open-label extension where all participants received Relyvrio. Long-term follow-up data showed that patients who received Relyvrio earlier in the randomized phase had better outcomes than those who initially received placebo and then switched to active treatment. This suggested that earlier intervention with Relyvrio may provide more benefit.
Phase 3 HEALEY Trial
The Phase 3 HEALEY ALS trial (NCT05021536) was a registration-enabling study that evaluated Relyvrio at the approved dose in a larger patient population. This multi-site trial used a seamless adaptive design allowing for interim analyses. The trial enrolled patients with clinically definite, probable, or laboratory-supported ALS diagnosed within 24 months of symptom onset.
Pharmacokinetics and Metabolism
Absorption
Following oral administration, both sodium phenylbutyrate and taurursodiol are absorbed through the gastrointestinal tract. Peak plasma concentrations are achieved within 1-2 hours for phenylbutyrate and 2-4 hours for taurursodiol. Food may reduce the rate but not the extent of absorption.
Distribution
Sodium phenylbutyrate is highly protein-bound and distributes throughout the body including the central nervous system. Taurursodiol has moderate protein binding and undergoes enterohepatic recirculation, which extends its half-life. Both compounds can cross the blood-brain barrier, though their CNS concentrations relative to plasma have not been fully characterized.
Metabolism and Excretion
Phenylbutyrate is primarily metabolized by hepatic beta-oxidation to phenylacetate, which conjugates with glutamine to form phenylacetylglutamine, excreted in urine. Taurursodiol undergoes conjugation with glycine and taurine in the liver. The metabolites are primarily eliminated renally.
Safety and Tolerability
Common Adverse Reactions
The most frequently reported adverse reactions in clinical trials included diarrhea, nausea, abdominal pain, and upper respiratory tract infections. These gastrointestinal symptoms often occur early in treatment and may improve with continued therapy. Dose adjustments may be needed for patients experiencing persistent GI side effects.
Serious Adverse Events
In the clinical trials, serious adverse events were similar between Relyvrio and placebo groups. These included respiratory complications, which are common in ALS patients regardless of treatment. Monitoring of respiratory function is recommended for all ALS patients.
Liver Function
Both components of Relyvrio are metabolized hepatically, and monitoring of liver enzymes is recommended periodically during treatment. Patients with pre-existing liver disease may require additional monitoring and dose adjustments.
Comparative Effectiveness
Comparison to Other ALS Therapies
Relyvrio joins riluzole and edaravone as FDA-approved disease-modifying therapies for ALS. These treatments have different mechanisms of action and can potentially be used in combination. Relyvrio's mitochondrial protective mechanism is distinct from riluzole's glutamate modulation and edaravone's antioxidant effects, providing a complementary therapeutic approach.
Future Directions
Research is ongoing to identify patient subgroups most likely to benefit from Relyvrio treatment. Biomarker studies are examining whether specific genetic or metabolic signatures predict response. Combination trials evaluating Relyvrio with other ALS therapies are planned.
References
Related Hypotheses
From the [SciDEX Exchange](/exchange) — scored by multi-agent debate
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- [Nutrient-Sensing Epigenetic Circuit Reactivation](/hypothesis/h-4bb7fd8c) — <span style="color:#81c784;font-weight:600">0.79</span> · Target: SIRT1
- [CYP46A1 Overexpression Gene Therapy](/hypothesis/h-2600483e) — <span style="color:#81c784;font-weight:600">0.79</span> · Target: CYP46A1
- [Circadian Glymphatic Entrainment via Targeted Orexin Receptor Modulation](/hypothesis/h-9e9fee95) — <span style="color:#81c784;font-weight:600">0.77</span> · Target: HCRTR1/HCRTR2
- [Selective Acid Sphingomyelinase Modulation Therapy](/hypothesis/h-de0d4364) — <span style="color:#81c784;font-weight:600">0.77</span> · Target: SMPD1
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- [Microbial Inflammasome Priming Prevention](/hypothesis/h-e7e1f943) — <span style="color:#81c784;font-weight:600">0.76</span> · Target: NLRP3, CASP1, IL1B, PYCARD
- [Blood-Brain Barrier SPM Shuttle System](/hypothesis/h-959a4677) — <span style="color:#81c784;font-weight:600">0.75</span> · Target: TFRC
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