Inclusion criteria:
Patients with a minimum age of 18 years and maximum 75 years at the time of informed consent
Patients who can read, understand, and provide written informed consent
Individuals with atopic dermatitis who have had a diagnosis for at least 12 months before to screening, as defined by the American Academy of Dermatology: Guidelines of care for the management of atopic dermatitis; Section 1. Diagnosis and assessment of atopic dermatitis
Patients with moderate to severe atopic dermatitis which is defined as having Eczema Area and Severity Index (EASI) ≥ 16, validated Investigator Global Assessment for Atopic Dermatitis (vIGA-AD) ≥ 3, and body surface area (BSA) affected ≥10%
Individuals who have a documented history of insufficient response to topical treatments (at least a moderate potency topical corticosteroids and/or cyclosporine for at least 4 weeks or the maximum duration recommended for the product prescribed) within the 6 months before screening determined by a dermatologist
Exclusion criteria:
Patients who are currently suffering from or have a history of any concurrent skin disorders that would interfere with assessments of the study medication's effect on atopic dermatitis. For example, psoriasis or lupus erythematosus or eczema herpeticum, or erythrodermic, refractory, or unstable skin disease, including, but not limited, eczema that requires hospitalizations and/or intravenous treatment for skin infections
Patients who have a known hypersensitivity to baricitinib or azathioprine or any component of these investigational products
Patients with any major concomitant disease that is expected to need the administration of systemic corticosteroids, such as unstable chronic asthma, or who otherwise interfere with trial participation or require active regular monitoring.
Patients who have been treated (1) Treatment with azathioprine in the previous 3 months (2) Having an experience of treatment with any oral JAK inhibitors including baricitinib < 4 weeks prior to randomization (3) Fusion proteins that target inflammatory pathways or monoclonal antibodies for less than 5 half-lives before randomization (4) Any parenteral corticosteroid administered by intramuscular/intravenous/intra-articular injection within 6 weeks before randomization or is anticipated to require a parenteral injection of corticosteroids during the study (5) probenecid at the time of randomization that cannot be discontinued for the duration of the study