A 22-year-old woman presents with a widespread, itchy, erythematous rash consisting of target lesions (dusky centre, pale ring, erythematous halo). The rash appeared acutely over the last 24 hours, mainly affecting her palms, soles, and extensor surfaces of limbs. She also has some blistering affecting her lips and oral mucosa. She started taking trimethoprim for a UTI 10 days ago. What is the most likely diagnosis?