Extension Study of Infigratinib in Children With Achondroplasia (ACH)

Key Rollover Participants Inclusion Criteria: 1. Pediatric participants ≥3 years old with ACH who have completed a previous QED-sponsored interventional study with infigratinib. 2. Participants and parent(s), legal guardian(s), or caregiver(s) are willing and able to comply with study visits and study procedures. 3. Participants are able to swallow oral medication. 4. Negative pregnancy test in girls ≥10 years of age or girls of any age who have experienced menarche. 5. If sexually active, participant must be willing to use a highly effective method of contraception while taking study drug and for 1 month after the last dose of study drug. 6. The PI, or a person designated by the PI, will obtain written informed consent from each participant's parent(s), legal guardian(s), or caregiver(s) and the participant's assent, when applicable, before any study-specific activity is performed. Key Rollover Participants Exclusion Criteria: 1. Participant has concurrent circumstance, disease, or condition that, in the view of the PI and/or sponsor, would interfere with study participation or safety evaluations. 2. Participants who developed a medical condition that will require the initiation of treatment with a prohibited medication. 3. Participants prematurely discontinued a prior QED-sponsored interventional study with infigratinib 4. Current participation in an ongoing clinical study with a sponsor other than QED 5. Participants that have reached final height or near final height. Key Inclusion Criteria for Treatment Naïve Participants: 1. Participants must be 3 to \<18 years of age at screening and have growth potential. 2. Participants and parent(s), legal guardian(s), or caregiver(s) are willing and able to comply with study visits and study procedures. 3. Participants are able to swallow oral medication. 4. Participants who have a diagnosis of ACH, documented clinically and confirmed by genetic testing. 5. Participants from PROPEL Study (Protocol QBGJ398-001) only: Must have completed at least a 6-month period of growth assessment in PROPEL prior to study entry. 6. Negative pregnancy test in girls ≥10 years of age or girls of any age who have experienced menarche. 7. If sexually active, participant must be willing to use a highly effective method of contraception while taking study drug and for 1 month after the last dose of study drug. 8. The PI, or a person designated by the PI, will obtain written informed consent from each participant's parent(s), legal guardian(s), or caregiver(s) and the participant's assent, when applicable, before any study-specific activity is performed. Key Exclusion Criteria for Treatment Naïve Participants: 1. Participants who have hypochondroplasia or short stature condition other than ACH (e.g., trisomy 21, pseudoachondroplasia, psychosocial short stature). 2. Participants who have significant concurrent disease or condition that, in the view of the PI and/or sponsor, would represent an increased risk to the participant or would interfere with study participation or safety evaluations. 3. Participants who have a history of malignancy. 4. Participants who are currently receiving treatment with agents that are known strong inducers or inhibitors of cytochrome P450 (CYP) 3A4. 5. Participants who discontinued treatment with prohibited medications for at least 5 half-lives before screening are eligible. 6. Participants who have received treatment with growth hormone, insulin-like growth factor 1 (IGF 1), anabolic steroids or any investigational or approved drug for the treatment of ACH in the previous 6 months. 7. Participants who have significant abnormality in screening laboratory results. 8. Participants who have had a fracture within 12 months of screening.