Open-Label study designed to assess the safety and plasma PK of tretinoin and relevant metabolites after topical dermal application of IDP-121 lotion.

Open-Label study designed to assess the safety and plasma PK of tretinoin and relevant metabolites after topical dermal application of IDP-121 lotion in subjects with moderate to severe acne vulgaris under maximal use conditions.

Key Inclusion Criteria:

• Male or female, between the ages of 9 and <17 years (16 years 11 months inclusive).
• Written and oral informed consent must be obtained. Subjects less than age of consent must sign an assent for the study and a parent or legal guardian must sign the informed consent.
• Subject must have a score of 3 (moderate) to 4 (severe) on the Evaluator's Global Severity Assessment at the screening and baseline visit in the facial area.
• Subjects with facial acne inflammatory lesions count no less than 20 but no more than 40.
• Subjects with facial acne non-inflammatory lesions count no less than 20 but no more than 100.

Key Exclusion Criteria:

• Use of investigational drug or device within 30 days of enrollment or participation in research study or concurrent study with this study.
• Any dermatological conditions on the face that could interfere with clinical evaluations acne conglobate, acne fulminans, secondary acne, perioral dermatitis, clinical significant rosacea, gram negative folliculitis.
• Any underlying disease(s) or some other dermatological condition of the face that requires the use of interfering topical or systemic therapy or makes evaluations and lesion count inconclusive.
• Subjects with facial beard or mustache that could interfere with any study assessments.