Hair analysis does not allow to discriminate between acute and chronic administrations of a drug in young children.

There are many differences between the hair from children and that of adult subjects, the hair being thinner, more porous with a different growth rate from the usual 1 cm/month observed in adults. In order to determine whether hair analysis could discriminate between chronic use and acute administration of a drug in children like in adults, we analyzed hair from 18 children aged between 1 day and 15 years in whom the administration of different drugs was known (single therapeutic administration or acute intoxication). A strand of hair was sampled within 1 to 45 days after treatment or intoxication. Analysis was conducted using LC/MS/MS. In the 10 youngest children, aged between 1 day and 29 months, the compounds administered in hospital or responsible for intoxication (lidocaine, ropivacaine, diazepam, midazolam, levetiracetam, morphine, ketamine, methadone, buprenorphine, THC, MDMA) were found in all segments of the hair independently of the time of sampling (1-45 days after ingestion). The concentrations detected were similar along the hair shaft, showing a radial diffusion and incorporation of the analytes in the hair of young children from the sebum. Concentrations could be very high when sampled shortly after administration (72 ng/mg for methadone, 75 ng/mg for MDMA after 3 days) and lower when sampling later (1.2 ng/mg for MDMA after 45 days). In these cases, hair analysis allowed to highlight the compounds responsible for intoxication even when they had disappeared from the blood or urine but should not be used to discriminate long-term exposure to a drug. In the eight remaining children aged from 34 months to 15 years, the drugs used in hospital (lidocaine, diazepam, morphine) or responsible for intoxication (THC, codeine, buprenorphine) were not found in any analyzed segments sampled 1 to 5 days after administration of the drugs, in agreement with the non-incorporation of the drugs from the sebum into the hair. For those children aged over 34 months, hair analysis allows to determine the chronic administration of a drug, like in adults.