This is an interventional, Pharmacokinetic (PK), Pharmacodynamic (PD), phase 1, open label study in children 6 to less than 12 years of age with ≥50% scalp hair loss due to severe alopecia areata. The purpose of the study is to collect data to support dose selection for subsequent studies in the same population.~Participants will be screened and, if all eligibility criteria are met, will receive the first dose of Investigational product within 28 days after the screening visit.~Participants will receive 20 mg ritlecitinib in one dose, daily, for 7 consecutive days. Blood samples for pharmacodynamic evaluation will be collected on screening and Day 7. Blood samples for pharmacokinetic evaluation will be collected on Day 7 at: 0 hr (pre-dose), 0.5 hr, 1 hr, 3 hrs, and 8 hrs after dosing.~At least 12 evaluable participants with respect to the primary endpoint will be enrolled in the study.~Participants and their parents/legal guardians will be required to visit the study site 3 times during the study (Screening, Day 1 and Day 7) A safety follow-up visit will be conducted by phone, 28 to 35 days after the last dose of ritlecitinib.
The purpose of the study is to evaluate the pharmacokinetics (how the medicine is changed and eliminated from your body after you take it) and pharmacodynamics (effects of the medicine in the body) of the study medicine (called Ritlecitinib) in children of 6 to <12 years of age with Alopecia Areata, a condition of scalp hair loss. 12 children with alopecia areata will be participating in this study. All participants will receive study medicine with a dose of 20 milligram (mg) orally once daily for 7 days. 5 blood samples will be collected on day 7 for pharmacokinetic evaluation and 2 blood samples each at screening and on Day 7 will be collected for pharmacodynamic evaluation. Participants will take part in the study for about 10 weeks.