Interventional Study of Infigratinib in Children < 3 Years Old With Achondroplasia (ACH)

This is a Phase 2, multicenter, randomized, placebo-controlled study to evaluate the safety and efficacy of infigratinib in participants \< 3 years old with ACH. The purposes of the SAD and Phase 2 portions are to identify and confirm the dose of infigratinib to be used in the Phase 2b portion, based on safety and PK. The purpose of the Phase 2b, placebo-controlled portion is to evaluate the safety and efficacy of infigratinib in children \< 3 years old with ACH at the selected dose.

Inclusion Criteria: * Diagnosis of ACH confirmed by genetic testing. If prospective participants had prior genetic testing, the diagnosis must be confirmed by a report from a certified laboratory, documenting the specific mutation. * Age 0 to 32 months (2 years and 8 months) at screening. * Signed informed consent, which must be obtained from each participant's parent(s) or legal guardian. * Parent(s)/Guardian(s) willing and able to attend all study visits and comply with all study requirements. * Parent(s)/Guardian(s) willing and able to comply with the routine care of the study participants according to local guidance for the management of infants and young children with ACH. * Able to swallow age-appropriate oral medication. * In participants \15 mg/m2/day of hydrocortisone or equivalent) or treatment with glucocorticoids at anti-inflammatory doses (for over 3 weeks within 6 months of the screening visit. NOTE: Low-dose topical, inhaled, or intranasal corticosteroids are acceptable. * Significant abnormality in screening laboratory results, * Allergy or hypersensitivity to any components of the study drug.