Drug Reactions and SJS-TEN
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Direct answer
Cutaneous adverse drug reactions span trivial exanthems to life-threatening severe cutaneous adverse reactions (SCAR) — Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN), drug reaction with eosinophilia and systemic symptoms (DRESS) and acute generalised exanthematous pustulosis (AGEP). SJS/TEN is characterised by epidermal necrosis with mucosal involvement at two or more sites, flaccid bullae and a scalded, eroding skin surface, most often from sulphonamides, anticonvulsants, allopurinol, nevirapine and NSAIDs. Management begins with immediate withdrawal of the culprit drug and, for severe disease, transfer to a burn-ward environment with fluid, electrolyte, nutritional, ophthalmic and aseptic supportive care.
What you must remember
- Maculopapular (morbilliform) exanthem is the commonest pattern, usually appearing within one to two weeks of a new drug and fading on withdrawal; urticarial, purpuric, lichenoid, photosensitive and fixed eruptions complete the mild spectrum.
- Fixed drug eruption: a well-defined round erythematous plaque, frequently bullous, recurring at the same site on re-exposure, classically on lips, genitalia and acral skin, healing with post-inflammatory hyperpigmentation; classical culprits — sulphonamides, tetracyclines, NSAIDs, metronidazole, anticonvulsants.
- SJS/TEN: prodromal fever and influenza-like illness, then atypical targetoid macules, flaccid bullae, positive Nikolsky sign and mucositis of eyes, mouth and genitals; SJS involves under 10 percent body surface area, SJS/TEN overlap 10–30 percent, TEN over 30 percent.
- Culprit drugs and timing for SJS/TEN: typically one to three weeks after starting the drug — sulphonamides (co-trimoxazole), aromatic anticonvulsants (carbamazepine, phenytoin, phenobarbitone), allopurinol, nevirapine and oxicam NSAIDs; HLA-B*15:02 predisposes Han Chinese and South-East Asian patients to carbamazepine-induced SJS.
- DRESS: onset two to eight weeks after drug start, with morbilliform rash, facial oedema, fever, eosinophilia, atypical lymphocytes and multi-organ involvement (liver transaminases, kidney); classical culprits — anticonvulsants, allopurinol, sulphonamides; treated by drug withdrawal with systemic corticosteroids in significant organ disease.
- AGEP: non-follicular sterile pustules on erythema with fever, settling within days of stopping the drug; beta-lactam antibiotics are classical culprits.
- SCORTEN assesses SJS/TEN severity using seven variables — age over 40, malignancy, tachycardia above 120 per minute, initial epidermal detachment over 10 percent, and raised serum urea, glucose and low bicarbonate — each scoring one point, with mortality rising with the score.
- Supportive care principles: stop the drug and all unnecessary drugs, manage in a burn unit or isolation, fluids and electrolytes, nutrition, gentle debridement with biological or paraffin dressings, mandatory early ophthalmology review, avoid prophylactic antibiotics and monitor for sepsis, and specific immunotherapy (such as intravenous immunoglobulin or corticosteroids) where evidence and local protocol support it.
Common confusion
SJS/TEN is most often confused with staphylococcal scalded skin syndrome, which also gives a scalded appearance with positive Nikolsky sign — but SSSS occurs in young children or immunocompromised adults, has superficial intraepidermal splitting, perioral crusting and flexural desquamation, and crucially spares the mucosae, because the split is intraepidermal; SJS/TEN always has mucosal involvement. Erythema multiforme major with mucositis is the second confusion — it is usually post-herpetic, shows true target lesions with three zones and more limited epidermal loss, and many authorities now separate it from SJS/TEN entirely.
Exam-focused takeaway
NEET-PG shows a photograph of eroded lips and targetoid macules with a drug history — carbamazepine or co-trimoxazole — and asks the diagnosis, the percentage detachment naming (SJS versus TEN) or the scoring system (SCORTEN). Fixed drug eruption is tested as a recurring lip lesion with hyperpigmentation, and DRESS as delayed onset with eosinophilia and liver involvement. "First step in management" is withdrawal of the offending drug — a perennially correct option. Learn the drug-timing-pattern triads, since options test all three jointly.
Frequently asked questions
How are SJS and TEN distinguished?
By the percentage of body surface area with epidermal detachment — SJS under 10 percent, SJS/TEN overlap 10 to 30 percent, TEN over 30 percent — with identical mucosal involvement and mechanism.
Which drugs most commonly cause SJS/TEN?
Sulphonamides, aromatic anticonvulsants (carbamazepine, phenytoin), allopurinol, nevirapine and oxicam NSAIDs; risk typically begins one to three weeks after starting the drug.
What is SCORTEN?
A seven-variable severity score for SJS/TEN — age over 40, malignancy, tachycardia over 120, initial detachment over 10 percent, raised urea, raised glucose and low bicarbonate — with mortality rising with each point.
What is the first step in managing SJS/TEN?
Immediate withdrawal of the suspected drug and every non-essential drug, followed by transfer to intensive or burn-unit supportive care; delay in withdrawal worsens outcome.
How does DRESS differ from SJS/TEN?
DRESS begins later (two to eight weeks), shows facial oedema, eosinophilia, atypical lymphocytes and internal organ involvement with little epidermal necrosis, whereas SJS/TEN is defined by epidermal necrosis and mucositis.
What is a fixed drug eruption?
A well-defined plaque that recurs at exactly the same site after each exposure to the culprit drug, commonly sulphonamides, tetracyclines and NSAIDs, typically on lips or genitalia, healing with pigmentation.