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PTC923

Phase 3

Phenylketonuria | Small molecule | Metabolic |PTC Therapeutics, Inc.|Last Updated: Jun 23, 2026

Target and mechanism

Molecular targetsepiapterin reductase
Target classEnzyme
ModalitySmall molecule

Success Probability

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Market & Valuation

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Trial Design

RandomizedDouble-BlindPLACEBO_CONTROLLED
Total Trials2
Total Enrollment357

FDA Designations

No designations recorded

Clinical trial landscape

PTC923 · 3 trials · 3 indications

Phase 3 2Phase 1 1
NCT05166161A Long-Term Safety Study of PTC923 in Participants With PhenylketonuriaPhenylketonuria
ACTIVE NOT_RECRUITING200 Analytics
NCT05099640A Study of PTC923 in Participants With PhenylketonuriaPhenylketonuria
COMPLETED157 Analytics
PHASE3ACTIVE NOT_RECRUITING
A Long-Term Safety Study of PTC923 in Participants With Phenylketonuria
PhenylketonuriaUnlock trial analytics
PHASE3COMPLETED
A Study of PTC923 in Participants With Phenylketonuria
PhenylketonuriaUnlock trial analytics

Study Endpoints

Primary Endpoints

Number of Treatment-Emergent Adverse Events (TEAEs)
Baseline up to end of study (up to 4 years)

A TEAE is any unfavorable or unintended sign (including an abnormal laboratory finding), symptom or disease in a study participant who is administered study drug in this study

Change From Baseline in Dietary Phe/Protein Consumption at Week 26, Measured During Phe Tolerance Assessment Period
Baseline, Week 26

Phe tolerance is defined as the total amount of dietary Phe (milligrams \[mg\]/kilogram \[kg\] per day) ingested while maintaining blood Phe levels within the range of 40 to 360 micromoles (μmol)/liter (L) (defined as ≥40 to \<360 μmol/L).

Part 2 Double-blind Phase: Mean Change From Baseline in Blood Phenylketonuria (Phe) Level to Weeks 5 and 6 (Averaged Over a 2-week Period) in Participants With Phe Reduction From Baseline ≥30% During Part 1
Baseline, Weeks 5 and 6 (average of the 2-week period)

Baseline was defined as the average of Day -1 and Day 1 predose blood Phe levels in Part 2, and mean level at Weeks 5 and 6 was calculated as the average of blood Phe levels collected during the Week 5-6 analysis visit window. Least square (LS) mean and standard error (SE) were calculated using mixed model repeated measures (MMRM) method.

Part 2 Double-blind Phase: Percent Change From Baseline in Blood Phe Level to Weeks 5 and 6 (Averaged Over a 2-week Period) in Participants With Phe Reduction From Baseline ≥30% During Part 1
Baseline, Weeks 5 and 6 (average of the 2-week period)

Baseline was defined as the average of Day -1 and Day 1 predose blood Phe levels in Part 2, and mean level at Weeks 5 and 6 was calculated as the average of blood Phe levels collected during the Week 5-6 analysis visit window. LS mean and SE were calculated using MMRM method.

Number of Participants With Treatment-Emergent Adverse Events (TEAEs)
From first dose of study drug (Day 1) up to 30 (±3) days after last dose of study drug (up to 50 days)

An adverse event (AE) was any untoward medical occurrence in a participant who received study drug without regard to possibility of causal relationship. Serious adverse event (SAE) was an AE resulting in any of the following outcomes or deemed significant for any other reason: death; initial or prolonged inpatient hospitalization; life-threatening experience (immediate risk of dying); persistent or significant disability/incapacity; congenital anomaly. AEs included both SAEs and non-serious AEs. TEAEs were defined as AEs that commenced or worsened after the first dose of study drug. A summary of other non-serious AEs and all SAEs, regardless of causality is located in the 'Reported AE section'.

Secondary Endpoints

Change From Baseline in Quality of Life (QOL) Using Phenylketonuria-Quality of Life (PKU-QOL) Questionnaire at Months 8, 14, 20, 26, 32, and 38
Baseline, Months 8, 14, 20, 26, 32, and 38
Change From Baseline in QOL Using the European Quality of Life - 5 Dimensions (EQ-5D) at Months 8, 14, 20, 26, 32, and 38
Baseline, Months 8, 14, 20, 26, 32, and 38
Palatability of PTC923
Month 1 Day 1
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Study Design & Arms

AllocationNA
MaskingNONE
ModelSINGLE_GROUP
PurposeTREATMENT

Treatment Arms

ArmTypeDescription
PTC923EXPERIMENTALParticipants will receive PTC923 7.5 mg/kg (participants 0 to \<6 months of age), 15 mg/kg (participants 6 to \<12 months of age), 30 mg/kg (participants 12 months to \<2 years of age), or 60 mg/kg (participants ≥2 years of age) orally once daily for a minimum of 12 months or until participant experiences lack of efficacy, adverse events (AEs) that lead to discontinuation, withdraws from treatment, or PTC923 is authorized and commercially available in the specific country.
Part 1: PTC923EXPERIMENTALParticipants will receive PTC923 7.5 milligrams (mg)/kilogram (kg) (participants 0 to \<6 months of age), 15 mg/kg (participants 6 to \<12 months of age), 30 mg/kg (participants 12 months to \<2 years of age), or 60 mg/kg (participants ≥2 years of age) orally once daily for 14 days.
Part 2: PTC923EXPERIMENTALParticipants will receive PTC923 20 mg/kg daily for Weeks 1 and 2, then PTC923 40 mg/kg daily for Weeks 3 and 4, then PTC923 60 mg/kg daily for Weeks 5 and 6.
Part 2: PlaceboPLACEBO_COMPARATORParticipants will receive equivalent quantities of placebo to match the 20 to 40 to 60 mg/kg dose escalation of the PTC923 treatment arm.
Cohort 1: PTC923 2.5 and 10 mg/kg/dayEXPERIMENTALParticipants will receive PTC923 suspension 2.5 milligrams (mg)/kilogram (kg)/day (dose divided in 2 for twice daily administration) orally for 7 days in Period 1, undergo a 3 (±1) day washout period, then escalate to a dose of 10 mg/kg/day (dose divided in 2 for twice daily administration) administered orally for 7 days in Period 2 (14 days total treatment).
Cohort 2: PTC923 5 and 20 mg/kg/dayEXPERIMENTALParticipants will receive PTC923 suspension 5 mg/kg/day (dose divided in 2 for twice daily administration) orally for 7 days in Period 1, undergo a 3 (±1) day washout period, then escalate to a dose of 20 mg/kg/day (dose divided in 2 for twice daily administration) administered orally for 7 days in Period 2 (14 days total treatment).

Interventions

NameTypeDescription
PTC923DRUGPTC923 powder for oral use will be suspended in water or apple juice prior to administration.
PlaceboDRUGPlacebo matching to PTC923
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Eligibility Criteria

Age Range12 Months to N/A
SexALL
Healthy VolunteersNo
Study Sites46

Inclusion Criteria: * Clinical diagnosis of PKU with hyperphenylalaninemia (HPA) documented by past medical history of at least 2 blood Phe measurements ≥600 μmol/L. * Women of childbearing potential must have a negative pregnancy test at screening and agree to abstinence or the use of at least one...

Countries:United StatesAustraliaBrazilCanadaCzechiaDenmarkFranceGeorgiaGermanyItalyJapanMexicoNetherlandsPolandPortugalSloveniaSpainTurkey (Türkiye)United Kingdom
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Competitive Landscape -Phenylketonuria 12 trials

Recent Changes (Last 90 Days)

LOWJun 23, 2026NCT05166161lastUpdatePostDate: changed
LOWJun 23, 2026NCT05166161lastUpdatePostDate: changed

Frequently asked questions about PTC923

What is PTC923 used for?

PTC923 is an investigational small molecule being developed for phenylketonuria (PKU) and BH4 deficiency, a rare genetic disorder causing hyperphenylalaninemia. It is in clinical development and has not been approved by the FDA. The drug is being studied in Phase 1 and Phase 3 trials for these conditions.

What does PTC923 target?

PTC923 targets sepiapterin reductase, an enzyme involved in the synthesis of tetrahydrobiopterin (BH4), a cofactor essential for phenylalanine metabolism. By modulating this enzyme, the drug aims to address the underlying metabolic defect in phenylketonuria and BH4 deficiency.

Who makes PTC923?

PTC923 is being developed by PTC Therapeutics, Inc., a biopharmaceutical company traded on NASDAQ under the ticker PTCT. The company is conducting clinical trials to evaluate the drug's safety and efficacy in patients with phenylketonuria and BH4 deficiency.

What phase is PTC923 in?

PTC923 is in Phase 1 clinical development for BH4 deficiency and has completed Phase 3 trials for phenylketonuria. It is an investigational drug, meaning it is not yet approved by regulatory authorities. A long-term safety study is ongoing, and the drug remains under clinical investigation.

What clinical trials is PTC923 in?

PTC923 has been studied in three clinical trials. NCT03519711 was a completed Phase 1 study in BH4 deficiency with 8 participants. NCT05099640 was a completed Phase 3 trial in phenylketonuria with 157 participants. NCT05166161 is an active, not recruiting Phase 3 long-term safety study in phenylketonuria with 200 participants.

Is PTC923 the same as CNSA-001?

Yes, PTC923 is also known as CNSA-001. In the Phase 1 trial NCT03519711, the drug was referred to as PTC923 (CNSA-001). This alternative name may appear in earlier research literature or clinical trial records, but both names refer to the same investigational compound.