When the Treatment Causes the Problem
A 34-year-old woman with newly diagnosed generalized epilepsy is started on carbamazepine by her family doctor. Within two weeks she develops a widespread blistering rash involving the mouth and eyes, fever of 39.1 C, and painful skin peeling over 15% of her body surface. She is admitted to the burns unit. Bloods show a white cell count of 2.1 x 10^9/L, ALT 180 U/L, and creatinine 130 micromol/L. She is on no other new medications. Her ethnicity is Han Chinese. The admitting doctor asks whether to continue carbamazepine at a lower dose and add an antihistamine, because the seizures have been well controlled.
1. Explain why continuing carbamazepine at a lower dose would be dangerous, and identify the likely diagnosis and its management priorities.
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Continuing carbamazepine at any dose would be dangerous because this presentation is not a simple drug rash. Widespread blistering with mucosal involvement of the mouth and eyes, fever, skin peeling over a large body surface area, and multiorgan involvement with leukopenia, transaminitis, and rising creatinine is consistent with a severe cutaneous adverse reaction, most likely Stevens-Johnson syndrome or toxic epidermal necrolysis. These are immune-mediated reactions in which the culprit drug must be stopped immediately; reducing the dose does not stop the process and can allow progression. Antihistamines treat itching but do not alter the disease course and may mask deterioration. Management priorities are: stop carbamazepine at once and document the allergy clearly; involve dermatology, ophthalmology, and the burns or critical care team; provide supportive care with fluids, electrolytes, temperature control, wound care, and pain management; assess the eyes daily for corneal involvement; monitor for sepsis, since the skin barrier is lost and the white cell count is low; and review all medications for other potential culprits. The epilepsy still needs treatment, but the alternative antiseizure medication must be chosen after specialist advice, avoiding aromatic agents such as phenytoin and lamotrigine that carry cross-reactivity risk. Genetic testing for HLA-B*15:02 is relevant in Han Chinese patients before carbamazepine, and this should be discussed with the family and documented.
2. The acute phase is managed and she recovers. Describe how you would approach her long-term epilepsy treatment and the professional practice issues raised by this admission.
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Long-term treatment requires a careful, specialist-led plan. Carbamazepine must be permanently avoided and recorded as a severe allergy in every record and on any alert system. Because cross-reactivity between aromatic antiseizure medications is a concern, the choice of an alternative such as levetiracetam, valproate, or lamotrigine should be made by neurology with the patient, weighing seizure type, teratogenicity, mood effects, and monitoring needs. If a high-risk aromatic drug is considered, HLA-B*15:02 testing may inform the decision in patients of Han Chinese ancestry, and the result should be discussed in context rather than treated as absolute. Seizure control should be reviewed with a clear plan for follow-up, adherence support, and safety advice about driving, swimming, and work until control is confirmed. The professional practice issues include the initial prescribing decision: carbamazepine was started without consideration of ethnicity-related genetic risk and without a clear plan for rash warning, which is a systems learning point. The patient should receive written information about warning signs of serious reactions, and the family doctor should be informed directly. Incident review and documentation are appropriate, and the patient should be supported to ask questions. Finally, consent and confidentiality must be respected when sharing information with relatives, and the patient's own account of what happened should be recorded.