High-dose methadone increases risk of neonatal syndrome
In a large cohort study of infants born to mothers prescribed methadone for opioid dependence, 45.5% needed pharmacological treatment for neonatal abstinence syndrome. The syndrome was more likely in the babies of women taking high-dose methadone, whereas those who were breastfed were less likely to need pharmacological treatment.
Infants born to mothers prescribed methadone represented 2.9% of hospital births, but used 18.2% of neonatal unit cot days.
Data were analysed from a large-scale retrospective cohort study over 3 years, covering 444 singleton live births to methadone-treated women in a maternity unit in Scotland. Mothers were identified following admission to the postnatal ward and data obtained by subsequent case note review.
Neonatal abstinence syndrome was diagnosed as withdrawal symptoms sufficient to warrant pharmacotherapy. Data were complete for 437 infants and 440 mothers, and basic demographic details were available for all births.
The mean maternal age was 28 years, and the median methadone dose 50mg daily (range 5-150mg). Maternal smoking was common, 80% had used illicit drugs during pregnancy, one in three had evidence of previous infection with hepatitis C, and social deprivation scores were very high.
The median gestational age of the infants was 38 weeks and 23% weighed less than the ninth centile. Breastfeeding was initiated in 27.7% of infants, and 11% were still breastfeeding on discharge from hospital.
In all, 45.5% of infants received pharmacotherapy for neonatal abstinence syndrome, and the median duration of morphine treatment was 11 days (range 1-44 days).
Factors associated with the development of neonatal abstinence syndrome included maternal use of benzodiazepines, and prescribed methadone dose; doses above 90mg daily were most likely to be associated with the syndrome. Breastfeeding for more than 72 hours significantly reduced the risk of neonatal withdrawal.
The duration of stay on the neonatal unit ranged from 1 to 108 days, with a median of 13 days, and 40% of admissions were primarily to treat neonatal abstinence syndrome.
Substitute prescribing of methadone to opioid-dependent women in pregnancy helps stabilise aspects of lifestyle, reduces some drug-related risks, and reduces the risk of pre-term birth and intrauterine growth retardation. Higher doses of methadone may be associated with less risky patterns of illicit drug use. However, they are also associated with a greater risk of neonatal abstinence syndrome. Pregnant drug-misusing women should be maintained on the lowest dose of methadone compatible with stability and supported to breastfeed their infants.
Dryden C, Young D, Hepburn M, et al. Maternal methadone use in pregnancy: factors associated with the development of neonatal abstinence syndrome and implications for healthcare resources. BJOG 2009;116: 667–673Reviewer
GP and Clinical Director, NHS Hull Social Inclusion Services