Which medication is most likely the culprit behind the diffuse tender erythroderma after starting therapy five days ago?

• A. Trimethoprim-sulfamethoxazole
• B. Amoxicillin
• C. Cephalexin
• D. Doxycycline

Answer: (A)

Severe drug-induced skin reactions can show up within days to weeks after starting a new medicine, and they often present as widespread, painful, red skin that may involve tenderness and sometimes mucous membranes. In this scenario, starting a new antibiotic five days ago with diffuse tender erythroderma strongly points to a serious cutaneous adverse reaction, most classically Stevens-Johnson syndrome/TEN.

Trimethoprim-sulfamethoxazole is a well-known trigger for these severe reactions, particularly because of its sulfonamide component. The immune system can mount a cytotoxic attack on keratinocytes in response to the drug or its metabolites, leading to widespread skin damage and detachment characteristic of SJS/TEN. While other antibiotics can cause rashes, they are less commonly associated with this severe, widespread, tender eruption, making TMP-SMX the most likely culprit in this presentation.

If this is suspected, discontinue the drug immediately and seek urgent medical evaluation, as SJS/TEN require prompt assessment and supportive care.