A 40 years old female is diagnosed to have epilepsy and is staed phenytoin and valproate. Four weeks later, she developed a diffuse rash all over her body, which gradually disappeared on stopping both the drugs. In how many weeks, will the rash reappear when she is re-challenged with phenytoin and valproate?

Ans: A. 1 day(Ref: Harrison 19/c p382, 18/c p3263; Goodman Gillman 12/c p592; Andrews' Diseases of the Skin: Clinical Dermatology By William D. Tames Timothy Berger, Dirk Elstoulp 113)Phenytoin Hypersensitivity Syndrome (PHS):Hypersensitivity due to anti-epileptic drugs.Type 4 Hypersensitivity reaction (Steven-Johnson Syndrome).Usually at 3-4 weeks.On re-challenging drug - pre-formed mediators released much quicker - Causes rashes - On same day of staing treatment.