Interpretation of hair findings in children: about a case involving carbamazepine

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This office has been recently involved in a case dealing with child custody, where the final outcome was difficult to establish. The following concentrations were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in the hair of a 21-month-old girl: 154 (0-1 cm), 198 (1-2 cm), 247 (2-3 cm), and 368 pg/mg (3-4 cm) after decontamination. Obviously, the concentrations measured in the hair were much lower than those observed in patients under daily treatment. In this sense, the frequency of exposures appears as infrequent (low level of exposure), with marked decrease in the more recent period. However, the girl was never prescribed carbamazepine and the mother, who was under carbamazepine therapy, denied any administration. The Judge asked if this could result from a single exposure and at which period. At least, three possible interpretations of the measured carbamazepine concentrations were addressed: (1) decrease in administration in the more recent period; (2) increase of body weight due to growing, so the same dosage will result in lower concentrations in hair; and (3) sweat contamination from the mother at the time the girl is with her in bed, the older hair being in contact longer with the bedding. In this case, it was impossible to conclude that the child was deliberately administered carbamazepine. The results of the analysis of hair could indicate that she was in an environment where carbamazepine was being used and where the drug was not being handled and stored with appropriate care. There are many differences between the hair from children and those from adults: hair from children is thinner and more porous, the ratio anagen and catagen phases are not maintained, and the growth rate can be different, at some periods, from the usual 1 cm/month. These differences, together with the influence of PK-PD parameters are reviewed in this paper, as a basis for suitable interpretation. In view of these results it is proposed that a single hair analysis should not be used firmly to discriminate long-term exposure to a drug when dealing with children.