Toxic epidermal necrolysis (TEN), an uncommon but potentially life-threatening skin reaction, is frequently induced by drugs. The mucocutaneous reaction is characterised by bullous detachment of the epidermis and mucous membranes. We present a 9-month-old male with methylmalonic acidaemia, generalised hypotonia, and global developmental delay. He presented with a 3-day history of fever, cough, shortness of breath, and vomiting. Eruption appeared after 5 days of vancomycin treatment. The eruption involved almost 60% of the total body surface area and both eyes. He was successfully treated with intravenous immunoglobulin (IVIG), antibiotics, and appropriate wound management and made a full recovery with negligible sequelae despite the severity of his disease. Important components of successful treatment include early recognition, intensive care, prompt withdrawal of the causative agent, early administration of IVIG, appropriate fluid resuscitation, and control of infection. IVIG might be beneficial in the treatment of TEN; however, controlled studies are needed to evaluate IVIG compared to other modalities.