The chronic use of opiate medications during pregnancy is a major public health challenge. Prolonged exposure to opiates in utero may result in withdrawal symptoms in infants commonly referred to as neonatal abstinence syndrome (NAS). Signs of NAS may include irritability, high-pitched crying, muscle tightness, seizures, diarrhea, vomiting, poor feeding, and unstable body temperature. Many infants may be treated by supportive (non-pharmacological) therapy by minimizing stimulation, cuddling, responding promptly to hunger cues, and other comfort care. However, some infants continue to show severe symptoms of withdrawal despite these interventions. In these cases, infants may be treated with medications (pharmacological therapy). Although it has been several decades since the first descriptions of NAS, there still remains limited information with regards to the most effective treatment. We hypothesize that medical treatment protocols of NAS with methadone can be optimized by better understanding what the body does to the drug (the population-based pharmacokinetics of methadone).

Inclusion Criteria:

1. Chronic in utero exposure to opiates
2. Term infant, greater than or equal to 37 weeks gestation
3. Failure of non-pharmacologic treatment of NAS
4. Infant meets criteria for pharmacologic treatment of NAS as determined by physical findings consistent with drug withdrawal and Finnegan scoring system
5. The attending neonatologist chooses to treat the qualifying infant with oral methadone.

Exclusion Criteria:

1. Prematurity
2. Congenital Abnormalities
3. Acutely ill neonates
4. Confounding medical illness necessitating therapy with opiates other than for NAS
5. Neonates whose only exposure to opiates were narcotics administered during labor
6. Infants who are wards of the state

Infants diagnosed with Neonatal Abstinence Syndrome and are treated with oral methadone.