Diagnosis of PKU, defined as documented presence of 2 mutant alleles in the phenylalanine hydroxylase (PAH) gene, of which at least 1 is the R408W mutation, as determined during Screening per the genotyping performed by the study central genotyping laboratory.
At least 1 plasma Phe concentration greater than (\>) 600 micromoles per liter (μmol/L) in the 52 weeks before providing informed consent.
Average concentration of plasma Phe \> 600 μmol/L in Phe samples taken during Screening, with no individual assessment below 360 μmol/L. Any Phe samples taken after Day -20 will not be included.
Body mass index (BMI) greater than or equal to (≥) 18.0 kilograms per meter square (kg/m\^2) to lesser than or equal to (≤) 35.0 kg/m\^2 and weight ≥ 50 kilograms (kg) at any time during the Screening Period.
Documented approval from a dietitian confirming that the subject can maintain their diet consistent in protein and Phe intake throughout the study as outlined in the Diet Manual.
You may not be if
Prior exposure to AG-181.
Receiving inhibitors of P-glycoprotein (P-gp) that have not been stopped for ≥ 5 days or a timeframe equivalent to 5 half-lives (whichever is longer) before administration of the first dose of study drug.
Receiving products that are strong inhibitors or strong inducers of cytochrome P450 CYP1A2, CYP2C8, or CYP3A that have not been stopped for ≥ 28 days before administration of the first dose of study drug.
Receiving treatment with an acid-reducing agent, including but not limited to proton pump inhibitors and H2 blockers. Short-acting acid-reducing agents such as calcium carbonate are permitted.
Any preexisting condition that could (in the opinion of the Investigator) interfere with gastrointestinal anatomy or motility that may disrupt the absorption, metabolism, and/or excretion of the study drug.
Any preexisting condition that could (in the opinion of the Investigator) interfere with hepatic or renal function that may disrupt the absorption, metabolism, and/or excretion of the study drug.
Inability to tolerate oral medication.
Unwillingness to washout from tetrahydrobiopterin (BH4) supplementation (eg, sapropterin dihydrochloride, Kuvan), pegvaliase-pqpz (Palynziq), or any other PKU therapy by Day -30 during Screening.
Clareo Health | A Study to Evaluate Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of AG-181 in Subjects With Phenylketonuria
