Interest of a Targeted Therapy for the Treatment of a Severe Form of Hypersensitivity to Drug (DRESS Syndrome)

Inclusion Criteria: 1. Adult patients (minimum 18year-old) 2. diagnosed at D0 (= baseline and inclusion) with DRESS defined by: 1. with a REGIScar score at D0 calculated at at least 4 (4 or 5: probable DRESS; \>5: definite case of DRESS), see Annex: REGIScar criteria 2. Skin eruption with an onset considered as compatible with a DRESS syndrome according to the investigator's opinion after the uptake of one or several drug(s) 3. AND Fever ≥ 38°C at the time of the examination or notion of a thermal peak ≥ 38°C in the preceding 72 hours. 4. At least 1 organ disorder compatible with the diagnosis of DRESS syndrome among the following disorders: * Adenopathies present in at least 2 different sites and ≥ 1 cm in size * Acute hepatitis defined by : * Elevation of liver enzymes in serum: ALAT (Alanine Aminotransferase) and/or ASAT (Aspartate Aminotransferase) * AND/OR an increase in serum total bilirubin, according to the standards of the local analysis laboratory (in the absence of a history of liver disease: ASAT and/or ALAT ≥ 3N (=3 times normal) * AND/OR total bilirubin ≥ 2N * Acute renal failure defined by : * An increase in creatinine according to local laboratory standards * AND a sterile cytobacteriological examination (in the absence of a history of renal disease: creatininaemia ≥ 1.5N * AND/OR increase in creatinine ≥ 0.3 mg/dl (or ≥ 26.5 mol/L) * AND/OR urine output \< 0.3 ml/kg/h (over ≥ 24h). * Pulmonary impairment defined by: * Oxygen saturation (SpO2) measured by pulse oximetry ≤ 95% in room air * And/or the presence of an interstitial syndrome on a standard chest X-ray or a CT scan of the chest (in the absence of any other cause of lung damage). 3. With eosinophilia (blood eosinophil count ≥ 500/mm3 or ≥0.5 G/L). 4. Patient having given written informed consent 5. patient with social insurance Exclusion Criteria: 1. Patients \<18 year-old 2. Patients with DRESS with REGIScar score \<4 3. Patients without skin eruption at baseline 4. Eosinophils blood count \<500/mm3 or \< 0.5 G/L at baseline 5. Patients with contra-indication to blood samples dedicated to the biocollection, according to the investigator's opinion 6. Patients with contra-indication to stop the culprit drug(s) involved in DRESS 7. Past history of hypersensitivity to biological drugs 8. Patients who received a previous anti-IL5 or anti-IL5 receptor therapy within 5 half lives (= 4 months) before inclusion 9. Patients with a contra-indication of topical corticosteroids (mainly a past history of contact eczema with clobetasol propionate) 10. Pregnancy and lactation