Q. A 38-year-old female who was treated for streptococcal pharyngitis 24 hours ago by her primary care provider with a single dose of intramuscular benzathine penicillin. She presents to the emergency department today with a worsening of her symptoms including fever, headache, muscle pain, and a skin rash. The patient is married with two children. She works as a bus driver and has a history of tobacco use and alcohol consumption. She also has a history of depression for which she is currently on medication. Her medical records also reveal that she was previously diagnosed with chronic syphilis infection. On physical examination, her temperature is 37.6 degrees Celsius (101 degrees Fahrenheit), blood pressure is 150/90 mmHg, heart rate 102/min, and her respiratory rate is 20/min. The patient’s pharynx is erythematous and slightly swollen, with exudate present on the tonsils. No cervical lymphadenopathy is noted. A diffuse macular erythematous rash was noted on her trunk and extremities (see image). Auscultation of her chest demonstrates clear lungs bilaterally, and her heart is in regular rhythm with a normal S1 and S2. No murmurs or rubs are heard. The patient reported muscle pain and joint stiffness, which is confirmed upon examination with joint swelling noted in her knees and ankles. A thorough neurological examination revealed normal cranial nerve function, normal motor strength, and normal reflexes. Based on this patient’s history and physical examination, which of the following is the most likely cause of her rash?