A 19-year-old male presents with severe nodulocystic acne affecting the face, chest, and back for the past 8 months. Examination reveals large, painful, deep nodules and cysts with evidence of post-inflammatory hyperpigmentation and early ice-pick scarring. Previous trials of oral doxycycline 100 mg twice daily for 3 months combined with topical adapalene and benzoyl peroxide have failed to achieve adequate control. The clinical picture marked **D** in the diagram represents the indication for which of the following therapeutic agents?