This is a Phase 2 open label study of ATI-2138 in participants with moderate to severe atopic dermatitis.

This open-label, single-arm study of ATI-2138 in moderate to severe AD participants between the ages of 18 and 60 years (inclusive) will investigate the safety, tolerability, pharmacokinetics, efficacy and pharmacodynamics of ATI-2138 administered over 12 weeks.

Inclusion Criteria:

• Able to comprehend and willing to sign the IRB approved ICF/assent prior to administration of study-related procedures.
• Male patients or non-pregnant, non-nursing female patients 18 to 60 years old, inclusive, at the time of informed consent/assent.
• Have at least a 1-year history of moderate or severe AD prior to the Screening Visit, and no significant AD flares for the 4 weeks prior to the Screening Visit as determined by the Investigator upon review of participant medical history.

Exclusion Criteria:

• Any prior exposure to systemic (oral) JAK inhibitors or TYK inhibitors at any time prior to Screening.
• Unstable course of AD (spontaneously improving or rapidly deteriorating) based on the patient history or as determined by the investigator during the Screening Period.
• Refractory AD (ie, AD that required frequent hospitalizations and/or frequent intravenous treatment for skin infections within the year before the Screening Visit).
• Concomitant skin disease or clinically infected AD or presence of other skin disease in the area to be dosed that may interfere with study assessments.
• Female patients who are pregnant, nursing, or planning to become pregnant during the study.