Can methadone concentrations predict the severity of withdrawal in infants at risk of neonatal abstinence syndrome?

AIM: To assess the usefulness of cord and serum methadone concentrations at 2 days of age in predicting the severity of neonatal abstinence syndrome (NAS) in infants whose mothers received methadone during pregnancy.

METHODS: After informed consent, infants were enrolled if they were delivered at 35 weeks gestation or greater. Relevant information was collected from maternal notes. A sample of cord blood was taken at delivery, with a follow up sample at 48 hours of age. The samples were analysed in batches, and the results were unavailable to the attending clinical staff. Infants were treated for NAS on clinical grounds according to a standardised scoring system.

RESULTS: Twenty five of 36 eligible infants over the 21 month period of the study were enrolled. Of these, 12 required treatment for NAS. Maternal methadone dose did not predict the need for treatment. However, infants who required treatment had significantly lower methadone concentrations in cord blood than the group who did not receive treatment (31 v 88 ng/ml respectively; p = 0.029). Paired blood samples for methadone concentrations were available for 17 infants. All but one of the 12 infants who required treatment had undetectable concentrations of methadone in the postnatal sample, whereas the median postnatal methadone concentration in untreated infants was 23 ng/ml (p = 0.002).

CONCLUSIONS: Methadone concentrations taken from cord blood may identify infants at greater risk of neonatal withdrawal and therefore requiring treatment.