A Study to Learn About the Study Medicine (Called Ritlecitinib) For the Potential Treatment of Severe Alopecia Areata (AA) In Children 6 To Less Than 12 Years of Age

Linear-log trapezoidal method was used for evaluation. For the calculation of AUCtau, pre-dose concentration of Day 7 was used as an estimate for the concentration of 24 hours post-dose on Day 7.

Clearance of a drug is a measure of the rate at which a drug is metabolized or eliminated by normal biological process. Clearance obtained after oral dose (apparent oral clearance) is influenced by the fraction of the dose absorbed.

Volume of distribution is defined as the theoretical volume in which the total amount of drug would need to be uniformly distributed to produce the desired plasma concentration of a drug. Vz/F is influenced by the fraction absorbed.

Elimination half-life (t1/2) is the time measured for the plasma concentration to decrease by one half at the elimination phase.

T lymphocytes included CD3 cells, CD4 T helper lymphocytes and CD8 T cytotoxic lymphocytes.

B lymphocytes included CD19 cells.

An AE is any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. Treatment-emergent were events between first dose to 35 days after last dose, that were absent before treatment or that worsened relative to pretreatment state.

An AE is any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. Treatment-related AE was any untoward medical occurrence attributed to study drug in a participant who received study drug. Relatedness was judged by investigator.

An AE is any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. 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.

An AE is any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention.

Vital signs evaluation included blood pressure and heart rate measurements. Clinical significance of any vital sign abnormality was judged by investigator.

Clinical laboratory parameters included haematology: haemoglobin, haematocrit, red blood cells count, platelet count, white blood cells count, total absolute: neutrophils, eosinophils, monocytes, basophils, lymphocytes; chemistry: urea and creatinine estimated creatinine clearance, glucose (fasting), sodium, potassium, chloride, aspartate aminotransferase (AT), alanine AT, total bilirubin, alkaline phosphatase, albumin, total protein; urinalysis: local dipstick: pH, qualitative: glucose, protein, albuminuria, blood, ketones, nitrites, leukocyte esterase and others. Clinical significance of any laboratory abnormality was judged by investigator.

The pediatric taste questionnaire included 3 questions regarding: 1) Overall Taste (likeability in tase), 2) Overall Mouthfeel (how the medicine felt) and 3) Overall Volume of Medicine (likeability of the amount of medicine). Each question ranged from 1 (most favorable) to 5 (least favorable), higher scores indicates less liking to medicine. Ritlecitinib was provided as capsules; for administration, the capsules were dissolved in water and the contents of the capsule in water were taken according to the dosing administration instructions.