A Long-term Study of the Medicine Called Abrocitinib in Children Aged 2 Years and Older With Moderate to Severe Eczema

Inclusion Criteria for the Extension Cohort:

1. Participants who have completed the treatment phase of the qualifying parent study (age 2 to <12 years old).

• No contraception methods are required for male participants. Female participants must not be pregnant or breastfeeding and, if the participant is of child-bearing potential, must use a highly effective form of contraception (i.e., abstinence) during the study intervention period and for at least 28 days after the last dose of study intervention.

Inclusion Criteria for the De Novo Cohort:

Age

1. Children aged 6 to <12 years at the time of informed consent/assent.

• No contraception methods are required for male participants. Disease Characteristics:

2. Participants who meet all of the following AD criteria:

• A documented diagnosis of chronic AD for at least 6 months prior to screeningand confirmed at screening and baseline visits according to the Hanifin andRajka criteria; and

• A diagnosis of moderate-to-severe AD at the baseline visit (must fulfill all ofthe following criteria: BSA ≥10%, vIGA ≥3, EASI ≥16, and WI-NRS ≥4); and

• Documented history (within 6 months of the screening visit) of inadequateresponse to treatment with topical medical therapy for AD (eg, TCS and TCI),for at least 4 weeks and are candidates for systemic therapy. Other Inclusion Criteria:

3. Body weight ≥15 kg

Exclusion Criteria for the Extension Cohort:

Medical Conditions:

1. Any medical or psychiatric condition including any active suicidal ideation in thepast year or suicidal behavior in the past 5 years or laboratory abnormality thatmay increase the risk of study participation or, in the investigator's judgment,make the participant inappropriate for the study. If the participant has SDQ total score ≥17, the investigator should exclude thechild or refer them to a pediatric MHP to determine if it is safe to participate inthe study. A copy or summary of the evaluation should be placed in the site sourcedocuments. Prior/Concomitant Therapy:

2. Required use of any prohibited concomitant treatments outlined in Section 6.9.3 andAppendix 9 of study protocol.

3. Required vaccination with live attenuated vaccines during study treatment and for 6weeks after discontinuing study treatment. Diagnostic Assessments:

4. Ongoing adverse event in the parent studies which in the opinion of theinvestigator, or sponsor, is an ongoing safety concern OR the participant iscurrently triggering safety monitoring criteria.

5. Discontinued from treatment early in the parent studies OR triggered adiscontinuation criterion at any point during the parent studies OR meets exclusioncriteria from the parent studies which in the opinion of the investigator, orsponsor, is an ongoing safety concern.

Exclusion Criteria for the De Novo Cohort

Medical Conditions:

1. Any medical or psychiatric condition including any active suicidal ideation in thepast year or suicidal behavior in the past 5 years or laboratory abnormality thatmay increase the risk of study participation or, in the investigator's judgment,make the participant inappropriate for the study. If the participant has SDQ total score ≥17, the investigator should exclude them orrefer the child to a pediatric MHP to determine if it is safe to participate in thestudy. A copy or summary of the evaluation should be placed in the site sourcedocuments.

2. Have any of the following medical conditions:

• Infections:

• Skin infections that require treatment with systemic antimicrobials within 2 weeks prior to Day 1 (baseline) or have superficial skin infectionswithin 1 week of Day 1.

• History of systemic infection requiring hospitalization or parenteralantimicrobial therapy or as otherwise judged clinically significant by theinvestigator within 1 month prior to Day 1.

• Have a history (single episode) of disseminated herpes zoster ordisseminated herpes simplex, or a recurrent localized, dermatomal herpeszoster.

• Infection with HIV, hepatitis B, and/or hepatitis C

• Evidence of active TB or inadequately treated latent TB.

• Skin Conditions:

• Including but not limited to psoriasis, seborrheic dermatitis or lupus on Day 1 that would interfere with evaluation of AD or response to treatment.

• Other Conditions:

• Documented history of skeletal dysplasia.

• Documented history of retinal detachment.

• History of or conditions associated with thrombocytopenia, coagulopathy orplatelet dysfunction.

• Prior history of leukemia, lymphoma, sarcoma or any other malignancy.

• Immunodeficiency disorder or a first-degree relative with a hereditaryimmunodeficiency.

• Any other medical conditions that in the investigator's judgment make theparticipant inappropriate for the study. Prior/Concomitant Therapy:

3. Prior treatment with a systemic JAK inhibitor for AD.

4. Live attenuated vaccination within 6 weeks prior to Day 1 or require vaccinationwith live attenuated vaccines during treatment or within 6 weeks after the last doseof study intervention.

5. Concomitant use of strong inhibitors and inducers of CYP2C19 enzymes and stronginducers of CYP2C9 enzymes is not allowed in the study. Prior/Concurrent Clinical Study Experience:

6. Previous administration of an investigational drug within 30 days or 5 half lives,whichever is longer, of Day 1. Diagnostic Assessments:

7. Hepatic and/or renal and/or hematological abnormalities defined as:

• AST >2 x ULN

• Hemoglobin <10 g/dL

• ALT >2 x ULN

• ANC <1000/mm3

• Total bilirubin ≥1.5 x ULN

• ALC <500/mm3

• eGFR <60 mL/min/1.73 m2

• Platelets <150,000 /mm3

Other Exclusion Criteria:

8. Investigator site staff directly involved in the conduct of the study and theirfamily members, site staff otherwise supervised by the investigator, and sponsor andsponsor delegate employees directly involved in the conduct of the study and theirfamily members.