Maximal Usage Pharmacokinetics and Safety of ARQ-151 in Children With Plaque Psoriasis (ARQ-151-216)

Inclusion Criteria: * Informed consent of parent(s) or legal guardian. * Males or females, 2 to 5 years old (inclusive). * Clinical diagnosis of psoriasis vulgaris of at least 2 months duration as determined by the Investigator or through subject interview. Stable disease for the past 3 weeks. * Psoriasis vulgaris on the face, extremities, trunk, and/or intertriginous areas involving at least 2% of BSA (excluding the scalp, palms, and soles). * An Investigator Global Assessment of disease severity (IGA) of at least Mild ('2') at Baseline. * Subject has adequate venous access for PK sampling in areas not involved by plaque psoriasis and not being treated with ARQ-151 (e.g., back of the hands). * In good health as judged by the Investigator, based on medical history, physical examination, 12-lead electrocardiogram (ECG), serum chemistry labs and hematology values. * Subjects and parent(s)/legal guardian(s) are considered reliable and capable of adhering to the Protocol and Visit Schedule, according to the judgment of the Investigator. Exclusion Criteria: * Subjects with any serious medical or psychiatric condition or clinically significant laboratory, ECG, vital signs, or physical examination abnormality that would prevent study participation or place the subject at significant risk, as judged by the Investigator. * Planned initiation or changes to concomitant medication that could, in the opinion of the Investigator, affect psoriasis vulgaris * Current diagnosis of non-plaq…