The PHOENIX Trial:
A Clinical Trial for People
Living With Amyotrophic Lateral
Sclerosis (ALS)

Learn about eligibility and more

About the PHOENIX trial

The PHase 3 PHOENIX trial (NCT05021536) will evaluate if the investigational drug, SOdium PhENylbutyrate and Taurursodiol (also known as ursodoXicoltaurine) is safe and effective as a treatment for adults living with ALS. Sodium phenylbutyrate and taurursodiol (ursodoxicoltaurine) is also known as AMX0035.

AMX0035 is not currently approved by the EMA. The trial will use a placebo as a way to compare the safety and effectiveness of AMX0035. A placebo is a substance that looks and tastes the same and is given the same way as the investigational drug being tested, but the placebo does not contain the investigational drug.

  • Pre-clinical
  • Phase 1
  • Phase 2
  • Phase 3
  • Phase 4

PHOENIX is a phase 3 trial, in which many persons living with ALS will be participating in both the United States and Europe. Because PHOENIX is a randomized, double-blind trial, individuals will be chosen at random to receive AMX0035 or placebo, and neither the doctors nor the participants will know who received the investigational drug.

What will the trial measure to evaluate if the investigational drug is safe and effective?

The PHOENIX trial will compare AMX0035 and placebo groups across several measures that are important in ALS.

  • Safety and tolerability
  • Function and survival
    • The Revised Amyotrophic Lateral Sclerosis Rating Scale (ALSFRS-R) will be used to assess and monitor key measures of functional status, such as: speech, handwriting, walking, and more
  • Breathing: Slow Vital Capacity (SVC)
  • Participant quality of life and health status
  • Time it takes to transition through ALS disease stages
  • Survival without requiring permanent breathing support

Caregivers will be asked to complete a questionnaire at the baseline visit and every 12 weeks during the trial. A caregiver is a person who regularly looks after and provides the necessary care for a person living with ALS. A caregiver can also be a professional, such as a hired personal assistant or hired nursing staff.

What should participants in the PHOENIX trial expect?

  • 48

    Each participant will be in the PHOENIX trial for approximately 1 year (48 weeks).

  • 60/40

    Participants in the PHOENIX trial will have a 60% chance of receiving AMX0035 and 40% chance of receiving placebo.

  • Study visits

    The PHOENIX trial is designed to be telemedicine-friendly; in-clinic visits will occur at the start of the study and every 3 months (12 weeks) after for a total of up to 6 in-person visits. All other monthly visits will be performed virtually.

  • Accessibility

    Some of the participating sites may arrange for shipment of the study drug to participants’ homes. For in-clinic visits, travel reimbursement will be provided.

  • Other meds

    If participants are taking riluzole and/or edaravone for ALS before the start of the trial, they may continue to take them during this trial.

    If participants are not already taking either medication, then they are not allowed to start riluzole or edaravone therapy during the trial.

  • Open Label

    Participants completing the 48-week trial will have the option to enroll in an Open Label Extension (OLE) Phase for up to 2 years, if not commercially available. During this phase, all participants will receive AMX0035 and continued safety and efficacy measures will be assessed.

What is AMX0035?1,2

AMX0035 is an oral, fixed-dose combination of sodium phenylbutyrate (PB) and taurursodiol (also called ursodoxicoltaurine; TURSO). AMX0035 is an investigational drug, also known as PB and TURSO.

How is AMX0035 administered to trial participants?

AMX0035 is a powder that comes in packets, which can be mixed with water and taken by mouth or through a feeding tube. Placebo will be administered in the same way.

Eligibility Criteria

Clinical trials have specific eligibility criteria to ensure that the goals of the study are met. Eligibility criteria differ from study to study.

The below are only select criteria for the PHOENIX trial. For a list of the full eligibility criteria for the PHOENIX trial please visit (NCT05021536). Select criteria includes:

  • Be at least 18 years old
  • Have been diagnosed with clinically definite or clinically probable ALS (Based on revised El Escorial criteria by a physician who is experienced in management of ALS)
  • Have started experiencing ALS symptoms within the past 24 months
  • Have a slow vital capacity (SVC) of at least 55% at the time of screening
  • If you are taking riluzole and/or edaravone as medication for ALS before the start of the trial you should be taking a stable dose at the time of screening and you may continue to take this medication during this trial (Participants are not allowed to start riluzole or edaravone therapy during the trial)
  • Does not need a tracheostomy or permanent assisted ventilation (PAV: > 22 hours of assisted ventilation daily for > 7 days)

PHOENIX Trial Locations

The PHOENIX trial is fully enrolled and is no longer accepting new participants.

The trial is well underway at more than 65 sites and 11 countries across Europe and the U.S. The latest information is available on

Click on the map below to see clinical site locations or click here to view a list.


  1. Paganoni S, et al. N Engl J Med. 2020;383:919-930.
  2. Paganoni S, et al. Muscle Nerve. 2021;63:31-39.doi:10.1002/mus.27091.