The proposed study is a single-center, observational and prospective study which will be conducted at the Pediatric Emergency Department, Geneva Children's Hospital.~This study will begin in January 2016 and will last one year. 53 patients are planned to be enrolled.~Children receiving oral tramadol as a pain killer at the emergency department, as part of their routine care, will be informed of the current study. Patients willing to participate will be included in the study after signing the inform consent (or respectively his/her parents or legal guardians). A unique oral dose of dextromethorphan (0.15 mg/kg) will be given to the participant for CYP2D6 phenotyping (T0).~Two hours later, capillary whole blood will be sampled to 1) measure the metabolic ratio dextrorphan/dextromethorphan (MRDOR/DEM) in order to determine CYP2D6 phenotype (validated metrics for CYP2D6 phenotyping), 2) measure tramadol and its active metabolite O-desmethyltramadol (M1), and 3) to genotype for CYP2D6. Saliva sample will also be performed to genotype for CYP2D6. Pupillometry will be performed before administration of tramadol, at T0 and then 1 to twice per hour, throughout the patient's stay at the emergency department.
Pupillometry will be performed before administration of tramadol, at T0 and then 1 to twice per hour in children having received tramadol as a pain killer as part of his/her routine care.~Pupillometry measurement will be correlate to CYP2D6 phenotype and CYP2D6 genetic score