A 32-year-old man with newly diagnosed HIV-1 infection (CD4 count 180 cells/μL, viral load 150,000 copies/mL) presents to the antiretroviral clinic. He has no prior opportunistic infections. Physical examination reveals oral candidiasis and mild hepatosplenomegaly. Baseline investigations show: ALT 45 U/L, creatinine 0.9 mg/dL, HBsAg negative, HCV antibody negative. The patient is counselled on adherence and started on a first-line regimen. After 2 weeks, he develops severe rash, fever, and facial edema. Which antiretroviral agent is most likely responsible for this adverse reaction?