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Study on the Long-Term Safety of PTC923 (Sepiapterin) for Patients with Phenylketonuria

Fast replyInvestigationalNo placebo
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What is this trial about?

A plain-language summary of the goals, design and what participants do

This clinical trial is focused on studying a condition called Phenylketonuria (PKU), which is a type of metabolic disorder. People with PKU have difficulty breaking down an amino acid called phenylalanine, which is found in many foods. The study is testing a treatment called PTC923, also known as Sepiapterin, which is taken as a powder by mouth. The purpose of the study is to evaluate the long-term safety of this treatment and to observe any changes in the participants' diet, specifically their intake of phenylalanine and protein.

Participants in the study will take PTC923 for a period of up to 24 months. During this time, researchers will monitor the safety of the treatment by checking for any side effects and conducting regular health assessments, including laboratory tests and physical exams. The study will also look at how the treatment affects the participants' quality of life and their ability to tolerate dietary phenylalanine. Some participants will be asked to complete questionnaires about their quality of life, depending on their age and language.

The study aims to provide valuable information about the safety and effectiveness of PTC923 in managing Phenylketonuria. By understanding how this treatment works over a longer period, researchers hope to improve the care and dietary management of individuals with PKU. The trial is open-label, meaning that both the participants and the researchers know which treatment is being administered. This approach helps in closely monitoring the effects of the treatment throughout the study.

The research process

The trial runs in 7 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Joining the study

    Upon joining the study, informed consent is required. This may include assent from children, with parental or legal guardian consent.

    Eligibility includes a clinical diagnosis of phenylketonuria (PKU) with specific past blood measurements.

  2. Step 2

    Initial assessment

    An initial assessment is conducted to establish baseline dietary phenylalanine (Phe) and protein consumption.

    Women of childbearing potential must undergo a pregnancy test and agree to use effective contraception during the study.

  3. Step 3

    Medication administration

    The medication PTC923 is administered as a powder for oral use.

    The dosage and frequency are determined by the study protocol and are specific to each participant.

  4. Step 4

    Ongoing monitoring

    Regular monitoring includes clinical laboratory tests, vital signs, and physical examinations to assess safety.

    Participants are required to maintain their current diet unless instructed otherwise by the investigator.

  5. Step 5

    Dietary phe tolerance assessment

    Changes in dietary Phe and protein consumption are measured to evaluate the primary efficacy endpoint.

    This assessment helps determine the impact of PTC923 on dietary tolerance.

  6. Step 6

    Quality of life assessment

    Quality of life (QOL) is assessed using specific questionnaires tailored to different age groups.

    These assessments are conducted in participants whose primary language is one of the specified languages.

  7. Step 7

    Completion of study

    The study is estimated to end by March 30, 2026.

    Participants are required to continue using contraception for up to 90 days after the last dose of the study drug.

Who can join the trial?

7 criteria

  • Provide informed consent, which means agreeing to participate after understanding the study details. If the participant is a child, parental or legal guardian consent is needed.
  • Both males and females of any age can participate.
  • Have a clinical diagnosis of **PKU** (Phenylketonuria), a metabolic disorder, with a history of at least two blood tests showing **Phe** (phenylalanine) levels of 600 micromoles per liter or higher.
  • Women who can have children must have a negative pregnancy test before starting the study. They must agree to avoid pregnancy by using highly effective birth control methods or abstaining from sex during the study and for 90 days after the last dose of the study drug.
  • Men who are sexually active with women who can have children and have not had a vasectomy must use a barrier method of birth control during the study and for 90 days after the last dose. They must also not donate sperm during this time. Men who are not sexually active do not need to use birth control unless they become sexually active.
  • Be willing and able to follow the study rules and procedures.
  • Agree to keep their current diet the same while participating in the study, unless the study doctor tells them to change it.

Who cannot join the trial?

10 criteria

  • Patients who have any other serious health conditions that could interfere with the study.
  • Patients who are currently participating in another clinical trial.
  • Patients who have had a recent surgery or plan to have surgery during the study period.
  • Patients who are pregnant or breastfeeding.
  • Patients who have a history of drug or alcohol abuse.
  • Patients who are unable to follow the study procedures or instructions.
  • Patients who have allergies to the study medication or its ingredients.
  • Patients who have a history of severe allergic reactions.
  • Patients who have a mental health condition that could affect their ability to participate in the study.
  • Patients who have a history of non-compliance with medical treatments.
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Investigated drugs

PTC923 (Sepiapterin) is being studied for its long-term safety in individuals with Phenylketonuria (PKU). This medication is intended to help manage PKU by potentially affecting the levels of phenylalanine, an amino acid that people with PKU cannot properly break down. The trial aims to observe how PTC923 influences dietary phenylalanine and protein consumption over time.

What is already known about the treatment

PTC923 (Sepiapterin) – This medication is administered orally and is currently being studied in clinical trials for its potential use in treating phenylketonuria, a metabolic disorder. The main therapeutic indication for PTC923 is to manage phenylketonuria by potentially improving the body's ability to process phenylalanine, an amino acid. At the molecular level, PTC923 works by providing a precursor to tetrahydrobiopterin, which is a cofactor necessary for the proper function of phenylalanine hydroxylase, the enzyme that breaks down phenylalanine. It is classified pharmacologically as a metabolic agent.

Investigated diseases

Phenylketonuria – Phenylketonuria is a genetic disorder that affects the body's ability to break down an amino acid called phenylalanine. This amino acid is found in many protein-containing foods and some artificial sweeteners. In individuals with phenylketonuria, phenylalanine builds up in the body, which can lead to a variety of health problems. If not managed, it can affect brain development and function. The condition is present from birth and is typically identified through newborn screening. Management involves dietary restrictions to limit phenylalanine intake.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2023-509229-31-00Protocol codePTC923-MD-004-PKUEstimated enrolment240 patientsSponsorPTC Therapeutics Inc.

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