• Safety: Infants will have continuous monitoring of vital signs, oxygen saturation, movements and adverse events to determine the safety of morphine.
  
• Pharmacodynamics: The Neonatal Infant Pain (NIP) and Premature Infant Pain Profile (PIPP) will be performed at baseline, (prior to drug administration)and at pre-determined time intervals after the dose to assess pain for the efficacy of morphine.
  
• Pharmacokinetics: The concentrations of morphine and its metabolites will be measured in plasma and urine at pre-determined time points and will be used to calculate the formation and elimination clearances of morphine and its metabolites.
  
• Pharmacogenetics: Impact of genetic variation in the UGT2B7 gene on the formation clearances of the morphine metabolites will be studied as well as the genetic variation in the µ-opioid receptor, COMT, and β-arrestin 2 genes on the PD of morphine use
  

The investigators hypothesize that identifying co-variates predictive of variability in morphine disposition and/or response will provide the scientific basis for rationale and individualized morphine dosing schemes in neonates and young infants.

60 preterm neonates ranging in gestational age from 22 to 32 weeks will be recruited from the NICU. Stratification by gestational age will be done to ensure broad representation. The decision to initiate morphine therapy will be based solely on clinical indications. Prior to morphine dosing, a biochemical assessment of hepatic and renal function will be obtained. A 0.05 mg/kg loading dose of morphine will be given by an intravenous infusion over 30-minutes in preterm neonates with a gestational age of less than 29 weeks, followed by a continuous infusion of 0.005 mg/kg/h, whereas a loading dose of 0.1 mg/kg will be given in preterm neonates with a gestational age of 29 weeks or more followed by a continuous infusion of 0.01 mg/kg/h. Pain assessment will be performed at baseline (prior to study medication administration) and at .5, 1, 2, 4, 8, 12 and 24 hours after the dose. At each of these time points infants will be videotaped for two minutes with two cameras. Videotapes will be scored afterward using standard validated pain assessment tools for preterm infants.